i used to have verizon UDP for a while, and them switched to Tmobile ones (because they have legal tethering). verizon is pretty fast, i got ~90mbps with iPhone 5. Tmobile really depends on location, in some places you get 60, 80, and in somewhere else you probably just get 'no service', especially while you are in a building. but wifi-calling on Tmobile helps a little bit.
my advice, if you are going to tether a lot, go Tmobile. (they have 5g free tethering, and 5g LTE+unlimited 2g mobile broadband plan for $10). if you are going abroad, go Tmobile (unlimited international data and text? it's ridiculous. though they claim you get 2g speed, but i get 3g in canada and china. and for $10 tethering plan, it's unlimited 3g international tethering!!! if you combine that with wifi calling, that's unlimited everything roaming FOR FREE. really, it's just ridiculous).
if you are traveling a lot (not internationally), go verizon. maybe Tmobile is good at your home, it may not be the same just couple blocks away.