Investing through an online broker is a slam dunk: It's easy and fees are reasonable. The hard part is zeroing in on the broker that's right for you. We surveyed 10 firms* and analyzed each in seven broad areas. Overall scores depend heavily on how much weight you assign each category. We weighted the categories based on what our readers consider vital: investment choices, 25%; tools, 20%; Web site and mobile functionality, 15% each; commissions and fees, and research 10% each; and advisory services, 5%.

Ultimately, you should decide what you consider most important and choose a broker accordingly. The best broker for you may not be the one that tops the charts. Your choice may boil down to the kind of investor you are. Active traders and new investors, for example, have very different needs and would likely prefer the services of different firms.

Take a look at our reviews of the following ten brokers to see which is the best fit for you.

1. Fidelity

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Fidelity earns the top slot, with the best mix of low fees, investment choices, tools, research and other criteria. It has the second-biggest no-transaction-fee fund program in our survey, offering 3,194 funds. (But if you want to buy a fund that is not on the NTF list, you'll pay about $50.) Fidelity also impresses with its massive muni-bond inventory and access to some IPOs.

When it comes to stock and fund research, Fidelity wins easily. It offers research from 21 firms, including Ford Equity Research and S&P Capital IQ. Customers can read 15 research reports about Apple and seven for the SPDR S&P 500 ETF.

Plus, Fidelity's managed-account port­folios can hold stocks, funds, ETFs, bonds and separately managed accounts. That range is enough to set Fidelity apart from other firms, such as Merrill Edge and TD Ameritrade, which offer managed portfolios that hold only mutual funds and ETFs.

2. Charles Schwab

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Best Broker for Mutual Fund and ETF Investors

The oldest brokerage in this survey (founded in 1971), Schwab tops the investment choices category for a slew of reasons. Among them are 4,968 mutual funds that customers can buy for no up-front load or transaction fee. The firm is also bulging at the seams with its lineup of 182 commission-free exchange-traded funds and even offers you some IPO action. Plus, it gets you access to 61 international exchanges. Some of those exchanges require broker assistance or a global account to trade, but there are no fees to open or maintain an account and no minimum-balance requirements. One negative mark: Buying a fund that is not on the NTF list at Schwab will cost you $76.

Clients want investment advice more than ever. And with an army of 800 certified financial planners, 3,000 registered representatives and more than 325 branches in the U.S., Schwab is giving it. The firm also offers research from nearly a dozen firms, as well as proprietary reports covering stocks, funds and the markets.

Though you need $250,000 to be eligible for Schwab's advisory services, those lucky customers have access to specialists in estate planning, options trading and fixed-income securities, in addition to customized investment advice. Schwab also got a boost from the range of its managed accounts. Clients can choose among a portfolio of mostly ETFs managed by Windhaven Strategies, a dividend-growth-oriented stock portfolio from ThomasPartners, and a portfolio that holds a mix of assets from the Schwab Private Client team, among others.

3. Merrill Edge

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Best Broker for Higher Balances

Tools such as online calculators, screeners and charts can help investors make wiser decisions. Merrill Edge trumps the competition in this category. The firm leverages research and data from its parent company, BofA Merrill Lynch, as well as S&P Capital IQ and Morningstar, to offer screens for ETFs, funds and stocks. It also offers screens for bonds and options. Its hefty calculator lineup helps customers with investing and personal finance issues, ranging from mortgage refinancing and college planning to IRA distributions.

You can open an account with $0 and pay $6.95 per trade. But high rollers get a better deal. Customers who have balances of $50,000 or more combined at Bank of America and Merrill Edge qualify for free trades on up to 30 trades a month. It's the only firm we surveyed to offer customers with higher balances a break on commissions.

4. E*Trade

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

The race is neck and neck among the well-established firms when it comes to who has the best mobile app. But E*Trade edges out the competition. In addition to handling stock, option and mutual fund trading, its app is set up for bond trading, a function none of the other apps offer. And E*Trade's app can be used with Windows and Amazon Fire phones as well as the requisite Android phones and iPhones. One other fun feature: You can scan a bar code of a product to find out whether its parent company trades publicly as a stock.

Also, E*Trade offers research from eight firms, including Credit Suisse, Thomson Reuters and Market Edge. Plus, it grants clients access to some of some of Morningstar's premium membership screeners, tools and analysis free.

You can open an account with a minimum $500. Standard trades cost $9.99 a hit.

5. TD Ameritrade

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Best Broker for Investors who Are Ready for the Next Step

TD Ameritrade offers a robust collection of investment options with 2,819 no-fee funds and 101 commission-free exchange-traded funds. But if you're hoping to buy a fund not on the NTF list, you'll pay about $50 extra, on top of the $9.99 stock commission.

In terms of tools, the firm offers the basics: a screener for mutual funds, ETFs and bonds, and portfolio reports that help you analyze your holdings. The site also has streaming quotes on the main dashboard, drag-and-drop customization and a virtual trading tool that allows customers to test investing strategies.

Most notably, TD Ameritrade offers two other platforms designed for more-sophisticated traders, Trade Architect and thinkorswim, which were not part of the survey. With no prerequisites, such as a certain number of monthly trades or assets to invest, it's easy for those who are ready to trade more feverishly to move to the next level. These sites offer loads of investing tools.

6. Scottrade

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Best Broker for New Investors

Investing newbies will appreciate the level of assistance offered by this firm. Scottrade won the top spot in the interaction category, which measured, among other things, user satisfaction with customer support by phone, in branches and on the Web. Scottrade has 500 branches nationwide, which helps, and it also scored well in the live phone support section of the study, says Mike Foy, who directs J.D. Power's wealth management practice. Online, the simplicity of Scottrade's dashboard is a welcome sight compared with the numerous widgets on other sites.

You need just $500 to open an account. Each trade costs $7 (although stocks under $1 have a different commission).

7. tradeMonster

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Another small firm proves to be a good choice for big traders. Like TradeKing, tradeMonster has no minimum requirement to open an account and charges just $4.95 to trade stocks and ETFs. Plus, being geared to more-active investors, the site scores top marks in terms of user-friendliness. In addition to customization, streaming quotes and easy-to-use order tickets, the firms also offer intricate charting capabilities.

TradeMonster also holds its own against the bigger firms when it comes to investing tools. It offers multiple stock screeners and a bond calculator that allows you to determine how sensitive your fixed-income portfolio is to interest-rate moves. But for the rest of your financial life, you're on your own. It does not offer tools that help customers decide whether to open an IRA or a Roth, or how much to save for retirement or for college.

8. TradeStation

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Best Broker for Active Stock Traders

Investors looking to buy stocks in bulk will find the best value at TradeStation. If you trade in 500-share lots, you'll pay $0.01 (yes, a penny) per share to trade the first 500 shares and $0.006 per share thereafter. Otherwise, you can choose a flat-rate commission ($9.99 per trade) or a sliding scale that cuts the commission rate the more you trade. In general, you'll need at least $5,000 to open an account, but other minimums apply for day-trading and other types of accounts.

But watch out for sneaky fees. TradeStation customers who fail to maintain a $100,000 balance or neglect to actively trade stocks or options will pay a whopping $99.95 monthly fee. TradeStation also charges a $35 annual IRA fee--no other firm in our survey has such a charge.

9. TradeKing

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

Hyperactive traders may be particularly drawn to TradeKing. It charges just $4.95 to trade stocks and ETFs. But you'll get nicked in other ways. The firm charges $100 or more to buy and sell 100 Treasury bonds, for instance, a trade that costs nothing at E*Trade, Fidelity or Schwab. Also, there is no minimum to open an account, but inactive accounts with a balance below $2,500 may be hit with a $50 fee.

Another drawback: investment advice is limited. But with an account of at least $10,000, you can get access to 10 preset, ETF-based portfolios designed for certain time horizons, investment objectives and risk tolerances.

10. Firstrade

OVERALL: Costs: Invest. choices: Tools: Research: Web site: Mobile: Advisory services:

The firm launched its brokerage services in 1985, and has clients in the U.S. as well as abroad. But it seems more geared toward those overseas clients, who live mostly in Asia. Firstrade has one branch in Flushing, N.Y. It lost ground against the competition in categories such as Tools, Research and Advisory Services. But its biggest drag came in Investment Choices: The firm offers only 473 mutual funds for no-transaction fee.

There is no minimum to open an account and stock commissions cost $6.95.

2012 Rankings

1. E*Trade
2. Fidelity
3. Scottrade
4. TD Ameritrade
5. TradeStation
6. Firstrade
7. Charles Schwab
8. Merrill Edge
9. Just2Trade
10. ShareBuilder

Kiplinger updates many of its best rankings regularly. Above is our 2012 rankings of best online brokers. Keep in mind that ranking methodologies can change from year to year based on what data was available at the time of publishing, changes to how the data was gathered, switches to new data providers and tweaks to the formulas used to narrow the pool of candidates.

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Nellie S. Huang is Senior Associate Editor at Kiplinger's Personal Finance magazine.