I wanted the ability to Tether and with Verizons Data Plans they include mobile hotspot. AT&T only includes it if you are on the $50 plan. I also wanted to try the Tmobile prepaid plans, they have a $35 / 3.5GB / 60 Day plan that looks like it would be great once their 1900 rollout is done. Testing tmobile where they do have 1900 coverage is very fast.
So basically with Verizon I get to choose between multiple carriers; Verizon if I need Fast LTE with tethering, AT&T if I want to use my own iPad sim or iPhone sim (if I'm being really cheap about it
or TMobile.
Also, since I already have an AT&T iPhone and iPad sim, I thought it would be good to get Verizon for some additional coverage.