Personally switched from VZW to Google Fi. It's on TMOs network. As you can imagine, when engaging with Google's support was hilarious when there was something I needed, but overall I don't miss Verizon and pay drastically less.
For those of us who have crappy coverage with TMO, Verizon themselves offer a much better alternative to their postpaid service, called Visible. It's pretty hilarious how much better of an experience it is, and you are on the same network.
Is Google Fi particularly cheap? Their normal prices seem to start at $35/month for 30GB of data which is more than Verizon's Visible plans at $25/month. (The current 50% off offer on Google Fi does seem a good deal though.)
I ended up switching to Mobile-X since I'm on wifi so much I only use a few gigs of data a month. $2/month + $1.90/GB vs Google Fi's flexible plan of $20/month + $10/GB.