"Ameritrade, sharebuilder.com, etc. maybe good for a trader who trades over a longer term and is not interested in getting the best price on the market. "
i would qualify the last part of the sentence to read "best price on the market at that moment"
daytrading with AMTD would be retarded, to put it simply. just the fact that it is not a direct access broker is reason alone, apart from the payment for order flow.
you are correct, in that AMTD is good for longer term stuff. i have AMTD and IB accounts (more than one of each).
AMTD is great, with the $3 per trade unlimited shares, when I want to set a limit order to buy or add to a position or close it out. as long as my timeframe isn't NOW, it's fine. i can wait (and have) weeks or even months) for a limit order to fill. that's fine when you are in the for the longterm and building positions in good stocks, which is generally how i play buy and holds. i wanna buy weakness and sell strength (generally) and can wait. time is on my side.
it also works pretty well for swings, although obviously swings are a bit more time sensitive.
daytrading with AMTD would be insane. now, the vast majority of my daytrades are futures, which AMTD doesn't offer, but even for stocks, it would simply be nuts not to use a direct access broker and (essentially) getting instant fills at the best price.
of course, anybody who doesn't have multiple accounts ANYWAY is crazy, but that's another story.