For anyone interested in learning more about both brokerages, here are some links and my opinion on both:
Scottrade Demo
Firstrade Demo
Scottrade vs. Firstrade
Overall, I'd say that Scottrade's the winner and that's where I'm headed. IMHO, they have a nicer site interface and I'm interested in using their price alerts. Although other sites have price alerts, I think this would be especially convenient to have this included with my brokerage account. The only thing going for Firstrade are their free mutual fund trading, their stock screener, and their ever so slightly lower trading commission. I especially like their stock screener because it isn't too big or too small and very useable. Fortunately, the free screener at Businessweek.com is even more comprehensive, so I won't feel too bad about not choosing Firstrade. I also don't invest in mutual funds and won't loose sleep over paying 5 cents more per trade with Scottrade.
Edit: I shouldn't completely dismiss Ameritrade as an online broker. They do have another business called Izone which offers 5$ market & limit orders. The commission is really great, but you have to qualify for it (2 years of online brokerage experience and a $5000 initial deposit). I don't know how legit this is, but it seems to be the most highly regarded online broker among the online investing community.