iPad: Which prepaid data plan is best?

[Selvers]

I'm planning on getting an ipad next year. I have wi-fi at home, but I'd like to use the web and play certain games while I'm away and there's no connection. So I'd like to get the data plan where you pay for a certain amount of data, and not the one where you pay every month for unlimited usage.

Which service do you think would be better for me, AT&T or Verizon? I heard with AT&T you can cancel and rejoin as often as you want; is it the same with Verizon?