great choice!( and I'm sure others will agree)
We love Bophut. The restaurants and bars are along one narrow street of converted Chinese shophouses. This is called Fishermans Village. The restaurants are of a high quality and the setting, sitting at your table looking out at the moonlit sea is very romantic! We were there two years ago and I'm sure there have been changes in the meantime but we found it ideal. Enough variety of places to visit in the evening and 10 mins in a taxi to the very busy Chaweng.
The only down side to Bophut is that although the beach is lovely to look at and relax on the sea does appear to feel "muddy" underfoot. We have only been to Koh Samui in July and August and it was good weather then, but does tend to rain quite often late afternoon and early evening - usually about 6pm.

I love Bophut too, I think it is the most authentic village in Ko Samui , there are some great eating places there- I like the Happy Elephant - I ust hope it does not become spoilt like other areas on the island.