TDA I don't have, but I hear great for research.
If you are looking for cheap commissions and a very nice respectable platform then I recommend optionshouse.com. It's a
$2.95 flat rate per buy!
I also have Scottrade. They are ok. It's $7 per trade over there.
But I'd for sure recommend
opening up a TOS account. All the professionals have them, and it's 100% free. Great free charting tools, live news, and many other features.
So right now I have a Bank of America account, a Scottrade account, an OptionsHouse account, and a ThinkOrSwim account.....Without a doubt follow the TOS link and get their platform, but for actual trading I'd recommend OptionsHouse.
Good Luck!!!