I have unlimited on the grandfathered Verizon unlimited plan. I use about 60-80gb a month, but I'm careful to go much higher, because word is that they will immediately terminate your plan if you reach 100gb. There's really no need to go that high, unless I spent a significant amount of time steaming video.
I use my phone for internet at home and on the road (unlimited hotspot), so I can justify maintaining the plan. Coverage while storm chasing is solid most of the time, although it gets spotty in parts of Colorado, western Illinois, North Texas and the Oklahoma panhandle.
Over the past few months I've noticed some glaring data slowdowns, but thankfully it's not all of the time and can usually be worked around by rebooting or flicking airplane mode off/on. I read somewhere that Verizon started throttling all plans last year and it's clear something has changed.
Still, I have no plans on switching carriers any time soon, because other comparable plans would be more expensive, have less nationwide coverage and/or feature much more throttling.