Koh Phangan is (I think) way prettier than Koh Samui, just because it’s so much wild nature! The bad part about that: it’s so mountainous that there is no way you can go with a normal motorcycle if you’re not used to it. So you have the option to go by Jeep-tours to discover the island and being there next time i would definitely do it. – At that time we just couldn’t stand being with 40 other tourists, so Koh Phangan turned out to just relaxing and no sightseeing at all.
We were there at the wrong time, so no full or half moon parties for us (it didn’t work out the way we planned it), but of course that’s what Koh Phangan is famous for and the island is ready to host hundreds over hundreds party lovers, not too idyllic of course.