t-mobile pay as you go - you have to order the SIM online.

there's also decent MVNOs but none offer LTE AFAIK. (well, maybe some do nowadays, but im not aware of them)

source: http://prepaid-phones.t-mobile.com/prepaid-plans

scroll down to "more plan options"

Also thats what ive been using for a while, i think its been there since a year or so.

My Verizon contract is up and I am really thinking about moving to Republic Wireless. The Moto G offers as much if not more than I want in a phone (I have a simple flip feature phone now) and I like that it uses wifi for voice which would make it feasible for me to use my phone at home (I live on the very fringe of cell coverage, and voice calls tend to have a lot of dropouts). Are there any other services I should consider?

When I decided to switch, I started here:

https://en.wikipedia.org/wiki/List_of_United_States_mobile_v...

and compared a couple dozen of them. My previous carrier was Virgin Mobile. The service is good, but they won't let you use a smartphone without a data plan, and their phone selection sucks. Republic has limited options too, but I wanted the moto x anyways.