First, let me say that I really like Chiang Dao. The people are seriously friendly, the landscape is epic, and there are some great things to see and do.
When I arrive I rented a motorbike and checked out almost every accommodation in the area. My favorite was Nature Home for the following reasons:
1) Clean spacious bungalow.
2) Comfortable bed.
3) Very friendly owners (who don't speak much english, but their daughter does if she is around).
4) Nice orchard setting.
5) Half way between town and the more remote cave area, which I found very convenient for doing both town stuff and nature stuff.
6) Best value for money that I found (I got a multi night deal of 500 baht per night).
CD Rainbow was also nice, but in a more remote spot (although with an epic view of the mountain over rice fields).
If you stay here be sure to check out the hillside temple near the cave (Wat Than Pha Pong), it is amazing.