RBoy
(www.rboyapps.com - Making SmartThings Easy!)
6
Depends on what features you want accessible through Smarthings. For example with Z-Wave thermostats you can get access to remotely locking the controls, setting filter reminders, setting upper/lower limits for heating/cooling, humidity reporting, C-Wire repeaters and so on.
See the first post of this topic as it summarizes the various features available in difference Z-Wave thermostats: