Tethering: Verizon or ATT hotspot compatibility recommendations?

Hello everyone,

I have couple of GL-MT1300(Beryl) and one GL-AR750S(Slate). I am thinking about purchasing hotspot eather from Verison or AT&T in US.
I like to hear from others about each cell company hotspot compatibility with above GL models, connected using USB, in a similat fashion like I am thetering using my iPhone connected over USB to GL inits.
I just checked and firmnware v4 is out. Do I need to upgrade orv3.x should work at well. I upgraded all units to the latest about month ago. Please list your cellilour models and your general epiriences and issues if any.