To add my thoughts into the mix, for a simple and good value system I went with Heatmiser Neostats after weighing up all the options. Mainly because they support underfloor heating, while Nest/Hive/Tado don’t. I have since integrated it into SmartThings and whilst the Heatmiser intelligence could be improved, I now have full control over everything through ST (and Alexa) so thats almost preferable for me.
Sorry to add further options and confusion to the mix.