Hi Image20
I prefer the girls in Phuket above the Koh Samui. Probably because there are a lot more bars and thus girls in Phuket.
On the other hand I find Koh Samui more laid back, and I do agree that there are a lot of non Asian girls (English, scandinavian) having holiday and they seem to be up for it as well. If you go to Samui you should pay a visit to the Reggae Pub and The Green Mango (both in Chaweng Beach), two quite good disco's. The big difference is that the food at Samui is more expensive than in Phuket, because the restaurants look more chique. Another nice thing at Samui are the beach bungalow hotels.
During my last two Thailand trips I first went to Bkk, then to Phuket (picked up my regular FL overthere) and then headed to Koh Samui.
If I would have to choose between the two I would pick Phuket, more lively accoring to me, and Phuket offers it all: beer bars, gogo, disco's...and lots of girls