Securities products and services offered by E*TRADE Securities LLC. Member FINRA/SIPC. Investment advisory services offered by E*TRADE Capital Management, LLC, a Registered Investment Adviser. Commodity futures and options on futures products and services offered by E*TRADE Futures LLC, Member NFA. Bank products and services offered by E*TRADE Bank and E*TRADE Savings Bank, both federal savings banks and Members FDIC. Stock plan administration solutions and services offered by E*TRADE Financial Corporate Services, Inc. All separate but affiliated subsidiaries of E*TRADE Financial Corporation.
In terms of volume, Interactive Brokers is technically the largest online stock trading platform in the U.S. It also advertises itself as the “lowest cost broker,” and for good reason: It only charges a startlingly low $0.005 per trade on stocks, ETFs, options, bonds, mutual funds, and futures (plus a 7 cent per contract fee for options). Technically, that’s still higher than Robinhood, but Robinhood only offers stocks, ETFs, and options (and as we noted above, Robinhood does skim some money off the top of trades via “payment for order flow”).
If you trade stock regularly, you might find yourself accidentally violating the dreaded wash-sale rule. This means you've sold shares of stock and then bought the same or similar shares shortly thereafter. This can cost you huge tax penalties. With a little planning, you can avoid this fate and still enjoy trading stocks aggressively with a little planning. 
In addition to attractive pricing, Ally offers a quality platform that gives you access to the entire universe of stocks and ETFs. Where some discount brokers focus on only one kind of trader (for example, options traders or high-net-worth investors), Ally Invest provides an excellent experience for investors of all kinds. A focus on discounted costs can sometimes be a red flag for quality, but Ally truly delivers with sophisticated calculators, profit-loss estimators, and more. Ally also offers a robust research library that incorporates visual slides and interactive media into its market data.

“I know stocks can be a great investment, but I’d like someone to manage the process for me.” You may be a good candidate for a robo-advisor, a service that offers low-cost investment management. Virtually all of the major brokerage firms offer these services, which invest your money for you based on your specific goals. See our top picks for robo-advisors.