ecobee4 vs. Nest
Mikah Sargent at iMore compares the two leading smart thermostats, the new ecobee4 and the Nest Learning Thermostat.
I have an ecobee3 at home, and several Nest thermostats at the office. I picked ecobee for its HomeKit integration, which Nest lacks. I also felt uncertain about Nest's future in the wake of their acquisition by Google.
While ecobee looks great, I love the dial design of the Nest. I think Nest wins on aesthetics. It's just so satisfying to use.
ecobee comes with a remote sensor, and you can add even more if you like. This really makes the smart thermostat a lot more smart, especially if your home HVAC does not have multiple zones. Its larger touch display allows it to show more info, like outside weather and the local forecast.
Both of these are nice products. It's a tough choice.