Laguna Phuket is not on the beach, it is across a busy road inland 1/4 mile. Still a very nice property (I personally prefer the Marriott resort on the north end of Phuket island see review: http://www.flyertalk.com/forum/Forum63/HTML/001416.html ). Laguna Phuket has decent nightlife as you are near the town of Patong.

Have not been to Krabi, but you access the resort via sea transfer which is only operated during daylight hours. No nightlife. Very tranquil! If to get away from it all, go for Krabi, but you will be isolated.