The U Chiang Mai is one of the nicer hotels in Chiang Mai and is a good choice if you don't mind the price.
The location is excellent, being in the middle of the old town and an easy walk (or bike ride - they have free bikes on hand for guests) to the main temples and a lot of great restaurants. If you stay on Sunday, there is a weekend market held in the evening. Interesting, whilst the street outside is reasonably busy the hotel is built in such a way that the rooms are very quiet.
The rooms have all been recently renovated and are very comfortable. The bed was the most comfortable of our trip in Thailand. The bathroom has all the mod cons and a great rainshower. We had the pleasure of our room opening directly onto the pool.
The breakfast was excellent, with a great buffet (including lots of fresh fruit) and a cooked to order main of eggs and some Thai and Chinese options.
There is a spa on hand, with some very good discounts given to guests. I'd recommend booking early, as it's quite small and if you are keen on a specific slot you may find it has already been booked.
My only reservation about recommending this place wholeheartedly (and why I am giving it 4 stars instead of 5), is the price. Whilst it was a very nice hotel, it fell short of being a great hotel. To pick some nits, the grounds were a bit small (which can make the pool area feel a bit claustrophobic) and the staff were professional but didn't go hugely out of their way to help. Overall, I felt they priced themselves a little bit high for what they offered. But in general, a very nice hotel and a good option.