I'm with T Mobile now. I don't know how AT&T thinks they can charge what they do. T-Mobile's network recently surpassed AT&T's in strength and they have faster LTE speeds than Verizon (AT&T and T Mobile use GSM while Verizon and Sprint use the slower CDMA). Plus Tax and fees included. And Verizon's call conferencing is unbearably bad.
https://opensignal.com/reports/2016/08/usa/state-of-the-mobile-network/
But I guess it depends on the area you live and work in.
LTE is a GSM product. Verizon uses CDMA for legacy products. If you have VoLTE on Verizon, 100% GSM. Have an older product, then yes, CDMA. Same goes for Sprint, except for voice.