Look, Phi Phi is an okay island - much more scenic than Samui which aint exactly shabby in this respect - but apart from the east coast it is starting to be a bit overcrowded and commercialised.
The problem is that it is not exactly in the Samui area - it's across the peninsula on the Andaman side, not Gulf - usually takes the best part of a day to transfer.
Now PHANGAN is only abt 20km from Samui and is arguably the best all round island in Thailand in that it has something to offer everyone from those seeking top resorts to people wanting old-style laid back beaches with el-cheapo bungalows.
And smaller Tao is only an hour or so north of Phangan - kinda similar on a smaller scale.
Got info/pix etc on all these places after several visits each HERE might help you.