Verizon or AT&T iPad 3G

well it doesn't matter,what does matter is the 3g frequency
and the ipad supports all the 3g frequencies (850 / 900 / 1900 / 2100)
so it should work well,just make sure that it's unlocked.

ILIA_93 wroteso what's the diffrence between the two?

Nothing. They are different providers, just like MTC and Alfa.

if you are panning to get a 3G ipad and use it here in lebanon, or the rest of the world except of usa, then get the ATT version which is the international version. Verizon's 3G ipad 2 uses CDMA (Code division multiple access) based network and carry data using 1xEV-DO technology. This would not work here in lebanon since lebanon uses GSM based network and carry data using HSDPA and HSUPA download /upload respectively. the verizon 3G ipad doesn't even have a sim slot since CDMA network uses a chip that emulates a unique code to identify the device.
So bottom line get the international 3G ipad, also known as the ATT variant.