Is there any website comparing 3G plan for both carriers? Like application fee, monthly fee (including different data usage limit), termination fee.
Macworld has a chart with a lot of that info here http://www.macworld.com/article/158361/2011/03/compare_ipad_data_plans.html
They also note (for your pre/post paid question):
As far as termination fee, neither are charging activation it looks like either (in the US). So you don't have to terminate it like a normal phone/data plan, you just pay for it the months you use it.