If you have a larger system, particularly one with rooms that are not used everyday, look at Honeywell Evohome.
It is the most expensive of the proven systems available - but it allows each room to be zoned independently.
Thanks I've had a look at Evohome but I think it's really too much for my needs. Yes I have a couple of bedrooms only in use when visitors come but turning down the TRVs cope with that.