As a functional garden ornament, the white painted WBC or a nice top bar would be hard to beat, though some are fond of their Beehauses. I've not been converted (yet) to the delights of the top bar or Beehaus, so personally I'd stick with a WBC, but get a 14x12 brood box for it as the standard one can be a bit pokey.
If not worried about looks I'd go for whatever was the standard locally (different parts of the UK favour Commericials, Nationals, Smiths, Langstroths etc), but again if National, I'd personally go for the 14x12 sized brood. You should also consider a polystyrene hive, cheaper and lighter, but again try and align its size with whatever the local favourites are.
The advantage of having the same size as your local beeks is that if you need to borrow a frame or get in a nuc or swarm, its much easier if the frames are compatible.