What thermostat works best with RA2 Select? System will have shades, lights and Sonos. No additional control system - will be controlled with Lutron app. Lutron app shows compatibility with Honeywell, Carrier, Ecobee and "works with Nest". What gives the best experience without leaving the Lutron app? Thanks.

I would assume that the Lutron stat would be the recommended one to use, no?

L-HWLV2-WIFI-WH

Lutron L-HWLV2-WIFI, for Lutron, by Lutron. I wouldn't use anything else with Select.

The Lutron thermostat looks very dated next to every other piece of tech.
Even their own literature shows their fugly thermostat alongside 3 slick looking alternatives:
[Link: lutron.com]
This is a retro job - thermostats are visible and will not be re-located. Aesthetics are important here.
So I guess the question is, what's the best option between the Ecobee, Honeywell and Carrier choices listed? I have no experience with any of the 3.

I would go with the Honeywell, since they have had a long term relationship with Lutron. I.e. they made Lutron's branded thermostats.

Is there any reason why you cant add any WiFi enabled thermostat such as a Nest, Honeywell or Ecobee?
How complicated is the heating & cooling system?

Effective 8/31/2019 the Lutron App will no longer support new Nest integrations.

That is the message you get when you try to add a Nest thermostat.

Is there a reason why they wont want to use the Nest app for the thermostat itself?