most people that are very active in the market don't have sharebuilder accounts. We have Interactive Brokers, OptionsXpress, Ameritrade, Scottrade, TradeKing, Etrade, etc, etc, etc.
We have those because they were first with the online trading stuff and the have the best applications, software, analysis tools.
The people I know who use Sharebuilder are folks who just want to put some money in their account on a regular basis and have it go to stocks or funds that they designate.
If you can buy and sell stocks, options, futures, mutual funds. Whatever you are interested in at any brokerage and get reasonable execution time then they are fine.
I am pretty sure you read the other posts on here about different brokerages. Check them out if you haven't