This article from AppleInsider compares the latest info on iPhone unlimited data plans from the major carriers:
In terms of the plans, I had the best pricing on T-Mobile when I had their T-Mobile ONE plan, but I had to switch to Verizon a while back (I’m on Beyond Unlimited) since T-Mobile scaled back coverage here, and I had to move to Verizon to get solid coverage.
One inaccuracy with the article: Apple Music is now free for Beyond and Above Unlimited Verizon customers (the six month free trial is still in effect for Go Unlimited customers).
Nathan Parker