As someone who is just starting to trade stocks, picking the best online broker is very important and is worth spending a little extra time comparing brokers side by side. What you will find is a pretty broad spectrum of commissions, quality of trading tools and quality of customer service.

Each year, publications review and rate online brokers and rank them across a variety of criteria to tell you who the best online broker is in each of the categories and then an overall ranking. For a beginner, you should only be concerned with the group called discount brokers. These are the online brokerages who cater to the individual trader by offering a web interface so they can make their own trades, along with research and analysis tools to help the investor make decisions about which stocks to buy.
 
This category includes many big names like E*Trade, TD Ameritrade, TradeKing, Scottrade, Zecco, etc. I am sure you have heard of many of these. Each one is good in their own way, each has their own particular strengths and offers services to attract a particular part of the market. Take TD Ameritrade as an example. They are not the cheapest and they don't have the best customer service. Where they differentiate themselves is with the quality, variety and sophistication of their trading tools. They attract more experienced traders who spend a lot of time on their stock trading, maybe even on a full-time basis.
 
The best online broker for a beginning trader is one who combines strengths in a few areas. One of these is cost. Beginners should look for a broker with a low cost structure, low or no minimum deposit requirements and strong customer service. This just makes sense. A beginner will go through a learning process early on, meaning they will place smaller trades more often. If they don't have low commissions, the fees will eat up any profits they do make.
 
Customer service is also important early on in your trading career. You may have questions about setting up your account, options for funding it, rules for making trades or understanding details like trading on margin. Having fast, responsive customer service is a quality of the best online broker and can make the difficult task of starting out much easier.