I had trouble with the thinkorswim website. It required me to lower my internet security and content advisor settings for my application to be processed. So I wasn't to happy with that situation. Customer service seems to be pretty responsive and were eager to help me. thinkorswim allows you to fax your application paperwork into them. I couldn't do that with Fidelity, I had to wait for the snail mail to work. Actually I sent it priority two day mail to a special address, but faxing is just a lot easier.
With the thinkorswim application you can logoff or get disconnected and still come back to the place in your application where you were. That was real nice. No data got lost, and I didn't have to redo everything all over again when I wanted or needed to go do something else.