Personally, I don't know why anyone with a modest level of financial planning understanding would want to go with Fidelity over Ameritrade (and why this thread is in MilesBuzz...).

Fidelity's trading commissions are higher and the bonus miles "cost" more than at Ameritrade. Ameritrade does charge for paper trade confirmations though (electronic ones are free). Not sure what Fidelity does in this regard. Also, Ameritrade doesn't do a good job with providing your real time account balance (although for most folks this isn't an issue).