I was on Samui about 6 years ago and stayed at the Boat House. It was a fun place to stay (we had the boat rooms), and the beach and coastline were very pretty.

There are some places on Samui where there are plenty of people, however there are also many places where you can go and be alone. As far as being commercial, it's not like there are neon CocaCola signs on the beach. When you are in a town, there are going to be all the normal "city" like features. The water is great, and there are some great day trips available from Samui.

Comparing to Krabi area -- I have been in this area twice in the past 4 years (last may is most recent). I have only stayed in the Railey beach area, which is striking. This area is pretty much void of commercialism (read neon), but has a bunch of hotel options, and can be overrun with longtail boats. I have also been on Lanta -- the island has much fewer places per sq mile (km) than other tourist locations, but also is missing some of the infrastructure that makes it easy to get around. Certainly less people here if that is what you are looking for, but also harder to find a variety of restaurants or facilities.

Hopefully the comments can provide some value without slant. Some people like the busy shopping streets such as Patong on Phuket, and others like being on an isolated place with no people. All choices are good, just depends what you are looking for.