What is the best way to get to Koh Samui from Phnom Phen?

I checked Bangkok airways, and its quite pricey, my other thought is taking Air Asia either to Bangkok, and then taking Bangkok air to Samui, or just taking Air Asia to Surat Thani. Or would it be better to fly out of Siam Reap to Samui? Or is there some land/ferry option that I don't know about? I am in the planning stages of a trip, so I am flexible.