I picked up several thermostats to test since my local HD carried them (either in store or free delivery). The ones I looked at were the Honeywell 8500 WiFi, CT50 WiFi, and Honeywell TH8320ZW.
The WiFi Honeywell seemed nice, but it only exposes the basic user interface elements to WiFi and they intend you to use it through their web site/cloud service. I found an API on GitHub that would make it work locally without using the cloud but did not test it. This model was not compatible with my specific furnace setup.
The CT50 seemed to be better as far as what was exposed to WiFi and had a good local API so you could work with it directly out of the box. It did not have a cloud service or anything so if you want to connect from a phone, you would have to figure out network settings. This thermostat was missing some critical settings and features for my furnace so it would not work.
The ZWave Honeywell was suggested as a working option for my furnace from Honeywell tech support but was missing a couple lines in the end. I do not have ZWave so I cannot say for sure if it would/would not work with HG. It has documentation in the PepperOne database so I assume that it would work with HG. It still only exposes certain items to ZWave, but the things it doesn't seem to be missing from that thermostat (compared to mine) anyway.
For reference, I currently have the non-connected version of the ZWave model (TH8320U) and it works quite well out of the box. It is a touch model that is monochrome (green/black) rather than the fancy LCD models. The model I have cost <$100 when purchased versus >$200 for the WiFi or ZWave version at the time. Today, the ZWave version can be had for ~$150 and the 8500 WiFi is $100 at HD (sale price). I plan on getting the TH8320WF which is a WiFi enabled version identical to my current thermostat. If I get it, I will use the following API on GitHub to communicate and link it to HG.
https://github.com/dattas/smartthings_radio_thermostatThis API may work with other model thermostats but having never tested it, I'm not sure it will work with the Honeywell even. Other comments indicate success.