I've always liked CS and their serious approach to health and wellbeing. It's also convenient(ish) to Bangkok. I always found service to be good to sometimes very good, but never exceptional.
I fine option as long as you realise that 1) Hua Hin is (IMHO) a crappy beach option compared to other spots in Thailand, and 2) you're in for a serious health boost (if that's what you're after)