Depends on what you want to do or what interests you have. There are 3 main beach/accom areas - Chaweng Beach, Lamai Beach and Bophut Beach with a reasonably newish super-luxury enclave of 4 hotels located at Manem Beach.
If ocean swimming is your thing, then forget Bophut. Chaweng is crowded and attracts all sorts from the families to young singles out for a good time in the night, but laze in the sun during the day. The Northern end of Chaweng is quieter than the south end, and not surprisingly this is where the majority of better hotels in this area are located. There is an Amari here, and the Amari's back in Bangkok are renowned for offering great airline rates. IIRC, their website has these listed.
You may want to have a look at the following link - I've used it before and not only does it show all accom from 200baht a night up to 1,000's per night, each property has pix and descriptions. There is also a general guide on the island, what to see, what each accom area can offer etc.
[URL=http://www.koh-samui-hotels.net/samui-island.htm[/URL]
For the most part Samui is still undiscovered by the masses and must be what Phuket was like before they found that piece of Paradise.

Cheers.