I've heard a lot of positive things about the Ecobee. I wonder if they track, cache or otherwise mine user Data through their App? That would be a big negative.
Ecobee tracks your usage data on their servers in order to provide reports to you. There is clearly some sort of aggregation of user data because it provides comparisons to other homes of similar size and location.
But Ecobee AFAIK doesn't sell that data to anyone, and they don't have an affiliation like Nest. You can always have a look at their privacy policy on the ecobee website to see if you're comfortable with the information that they do collect. https://www.ecobee.com/legal/use/ My personal take, and YMMV, is that they don't collect more information than needed to provide the services the device offers.