I can't say that I am "experienced" although I have been investing in stocks/options since 1999. I currently use Fidelity for my retirement accounts. I have 2 Etrade accounts. I just recently opened an account with optionsxpress. Reasons: I wanted to keep my retirement accounts separate from my other accounts. The commissions are a little higher but my trading is somewhat less. Also, there is a brick/mortar office within 30 minutes so if I have a problem I can get in someone's face.
Etrade: I like the website and because I have become accustomed to it, navigation through the site is easy for me. Optionsxpress because they offer portfolio margin. It seems like the commissions are slightly lower as well.
I have used Schwab and Ameritrade in the past. Not that they were bad, but I just moved funds from Schwab to Etrade about 7 years ago. Ameritrade was fine. As you can see, everything I like to do is online.
I use Ameritrade (since the 90's) and optionsXpress since the first year it opened. They are both excellent. As MJ states, other services are better for a day trader such as TradeStation or CyberTrader. Brokers like these require approx. 40k shares traded each month to qualify for their best plans (per share structure).
I use USAA and Sharebuilder. Both work for me. Sharebuilder didn't have great customer service when I called them to confirm information on my Sharebuilder tax statement. I currently have nothing in that account.
I use Choice Trade. I have a small portfolio and they offer $5 trades. I have not had a problem with them in the last 3 years. The system is easy to use but it is stripped out so no bells and whistles. I like E-trade's platform but I can live without it.