There is no perfect system.
EPH works best with zones using OpenTherm. But does not like to TRV heads.
Hive uses heat on demand, but it seems the hub is not very powerful and some times a more powerful hub is needed to make the RF work, also reports on the TRV heads not being very strong, and has no Opentherm.
EvoHome does not have Opentherm as standard it is an add on module.
Drayton Wiser it seems has the best TRV heads able to work out when to close so can raise a room to new temperature faster than the others.
Nest does not link to any TRV heads, it did link to Energenie heads but support withdrawn. But is OpenTherm.
I am not convinced the wall thermostat needs to link to the TRV heads, I use Energenie and eQ-3 heads neither are linked to my Hive. I have had problems with Nest Mini acting like a naughty boy, switching off lights when not told to, then refusing to turn them back on, up to now it has not altered room temperatures which in theory it could do with the Nest wall thermostat and Energenie TRV heads.
It is all well and good asking others how their system works, however people tend not to admit when it goes wrong or is missing something. I have asked a few with Hive how well it controls individual rooms, after saying how good it is, only to admit they only have half a system and no TRV heads fitted.
So my own is only one I can talk about, the eQ-3 bluetooth heads for the TRV's have worked very well considering only £15 each, the Energenie TRV head does not have window open feature, but does connect to internet so I can see the room temperature when away, allowing me to turn on the stand alone AC to cool room before return, likely they would work with IFTTT to auto turn on AC but this year AC used for around 20 days and only had to turn it on before returning home 3 times, so hardly worth the effort to automate it.
The Nest Gen 3 thermostat did what I wanted controlling the boiler with just 2 wires both for CH and DHW, however as to temperature control as in the hall which has stairs I have to set it to heat last few degrees at 0.5°C per ½ hour or it will over shoot, so works OK while home, but when we go out on return have to manually turn down or it over shoots, but it does geofence well and the problem is more down to house design than Nest.
Much depends on what you want, I found in last house Energenie TRV heads with a modulating boiler worked well, but took some setting up, and never ever bothered fitting a smart thermostat, the TRV heads did the job with out needing one, this house used an oil boiler which is not modulating and not had much of a problem, however Energenie TRV heads do have an over the top anti-hysteresis software package so have to cheat and set to 22°C for and hour then drop to 20°C in morning or it is 11 am before rooms at 20°C.
Although we can and do turn rooms down, we find no room really gets cold, and really you need over sized radiators to select when each room is heated, house built into hill side so some rooms never get really cold in winter or hot in summer, design is good as naturally the kitchen is coolest room in summer. Main problem is living room too big, two settees and 4 electric reclining chairs in it gives idea of size, so slow to heat or cool, we can hold the room temperature down in summer to around 25°C but the 750 watt AC is not big enough to cool room once it warms up.
We are told people before us lived in flat under main house in winter as cheaper to heat. And just used 4 rooms. But it all depends on the house which will work best, and of course the boiler and radiator sizes, with over sized radiators you can arrange so rooms are heated in order required, but our radiators are not big enough, so if we set more than ½ hour delay room to room, the boiler simply switches off, it does not heat rooms any faster. Remember we have oil, so boiler does not modulate.
