Where to Stay
Make sure you stay in Chaweng! It is easy to end up at some all-inclusive family resort.Arc Bar is very popular and has a great pool that plays tech house all day. If you want a cheaper alternative there are a bunch of hostels in the area.
Where to Party
Every night most tourists end up at Green Mango, a huge nightclub complex with multiple rooms. It is a great spot for meeting other travellers. The biggest problem with Koh Samui is that the bars/clubs have to close by 2 a.m. However, if you look hard you can find some after-hours places near Green Mango (just walk down the small bar strip and follow the crowd). There are many clubs here that claim to be busy every night, but I found that the Mango was the only good rage. Ark Bar has beach parties twice a week and is generally busy most nights. However, this place is only good for starting the evening, unless you like sitting down all night and watching fire twirlers. Bar Ice is a huge tourist trap – only go here if you are really interested in seeing an all-ice bar, but I guarantee you won’t spend more than 15 minutes here (and there is a cover charge).
Green Mango plays Top 40 and some decent house. At the after-hours places you can hear some really random nineties rock (which is actually really cool in the wee hours of the morning). Ark Bar plays awesome tech house during the day and at night.
During the Day
Not much to do during the day, but you can find decent scuba diving. Most people chill by the beautiful beach or Ark Bar pool all day.
Koh Samui is a lot more expensive than its neighbouring islands (Koh Tao and Koh Phangan) and also attracts a lot of vacationing families. The party is great at night, but I wouldn’t stay on the island for more than a couple of nights.