@Mbhforum, there are a lot of ST users out there that are using ecobee thermostats (smart, smart-si, ecobee3, and even EMS) with my custom ecobee device that I created which adds most of the rich API functionalities compared to the ST stock device.
See
I’m currently working on adding reporting & stats capabilities so that ST users with ecobee can later post their daily runtime stats on their devices (HVAC, fan, humidifier, dehumidifier, HRV/ERV) to some analytics platforms such as grovestreams (www.grovestreams.com) and make any possible correlation with their sensors.
It seems that ecobee thermostats are more reliable, and with their latest addition (ecobee3), they have more capabilities than Nest out-of-the box. On top of that, there is less fuss about data retention issues.
Ecobee’s API are really rich (sometimes too much to my taste), but with my Custom Ecobee Device you can really use most of them within the ST environment.
And, finally I have developed a lot of smartapps that can take advantage of ecobee within SmartThings.
Refer to GitHub - yracine/device-type.myecobee: SmartThings-ecobee integration
My 2 cents.