Which Nest smart Thermostat should you buy? We compare the latest two models the 3rd generation Learning Thermostat and the more recent Thermostat E Should I Buy The Nest Thermostat E Or Nest Learning Thermostat (3rd Gen)? Which Nest you should buy depends a lot on where you are. In the US, the E is almost a no-brainer: it's $80 cheaper, offers almost exactly the same features, and takes