In reply to chrisclimber:
I've spent alot of time in the area there over 3 separate trips. The last time was for 6 months earlier this year.
Ton sai and Railay themselves are very busy, some of the climbs are very polished and there is a lot of trash lying around, but even with all that the climbing is great.
Plus: there is a lot more to the climbing in the area than Tonsai and Railay nowadays. Koh Yao Noi has some of the best climbing in Thailand and there are some newly developed crags in beautiful surroundings with no polish or rubbish within a 10 minute scooter ride of Ao Nang.
There is also Koh Laoliang a bit further south (half day journey from Krabi). Absolute paradise and not a bit of polish, no longtail traffic, no rubbish no crowds, Just a beautiful paradise island with some truly superb climbing.
My advice would be to stay in Tonsai or Railay for only a part of your trip. This will allow you to conveniently access a pick of the routes there. Make sure you check out the other spots as I reckon you'll prefer them, unless you're just looking for a party scene with a bit of climbing thrown in once the hangover subsides (in which case Tonsai would be best!).