New iPad - Verizon vs AT

I'm about to upgrade from an original AT&T iPad to a Retina iPad. When I got mine the only cellular option was AT&T.

Now with the propagation of 4G networks and Verizon iPads without the MiFi, can anyone give me pros & cons overall

for which WiFi/Cellular to get?

AT&T vs Verizon?

Thanks much

Steven