I've switched 3 of my 4 nests to a z-wave thermostat and I'm really happy[1] with it so far. The Honeywell T6 pro. I got them used for about $56 each and they were in near-perfect condition.

[1] With one exception, which is really niche to me: The T6 has what looks like a PID-style control algorithm hiding in it, and instead of specifying a deadband between on/off, you can only specify a max number of cycles per hour. I already have a home-brewed PID algorithm controlling the temperature target of my boiler, so I actually _want_ a stupider thermostat that will stay on/off a little longer. But this is purely because I'm weird. The T6 is really good at keeping the temperature on target, and the homeassistant integration was fast and easy and has been totally solid. I recommend - I'm just waiting for the last one to arrive and I will have completely replaced my Nests (gen2 + gen3).

I'll also add that the local UI on the T6 is much better than the one on the nest. And the installation process was really simple -- Honeywell clearly learned from Nest on this one, and then beat them with the UI. I'm really happy with the upgrade, even though I'm totally annoyed with Google for wrecking my perfectly functional thermostat.