Deciding on Android Phone which will work on T-Mobile and AT&T Pre-Paid



New User here at the verge.

I recently got an International version of HTC Incredible S S710e Version.

I am currently a AT&T Post Paid customer(Contract finished and going on a month-month basis) and wish to move to the pre-paid world.

I dont use my minutes much and rarely SMS. I would Love to use the Data Service though I use WiFi at home.

Considering the bands and frequencies differences (which makes me going to T-Mobile tough as my phone has only 2100 AWS Band and not 1700 Band), What Phone do you think would be better for me so that I can go to AT&T or T-Mobile as and when I want as I will be strictly in the Pre-Paid world?

I Love Android and I am only thinking about Android phones only (No iPhone or Windows phone)

Currently I can see only Galaxy Nexus (GSM Phone on the Play Store) which is a penta band phone.

Do you suggest I buy the GN phone or wait for upcoming Nexus phones sometime this year and adjust with my HTC till then with At&T prepaid?

Are there any other android phones which will work on both T-Mobile and AT&T prepaid?

Please advise.