Been super happy with ecobee 3 lite which you can install without a c-wire unlike some others.
Also it's pretty cool that you can go on the website and download data about your system. The log will show, at 5 minute intervals for the entire time period, whether the system was on, what it is set to on thermostat, temperature inside, humidity, temperature outside, how long it ran during that period in seconds, and the temperature data for your other sensors. We found it useful in looking at what effect replacing all of the single pane windows in our house had during the summer. Turns out the effect on total runtime wasnt that big but temp was maintained much better.