Most efficient route to explore Phuket, Koh Samui, Koh Phi Phi, and Krabi?

Hi, beginning from Bangkok what is the most efficient route to travel to Phuket, Koh Samui, Koh Phi Phi, and Krabi? We're planning on using train for the majority of (if not all) transportation and are fully prepared to spend many half days on trains. We need to end in Bangkok again as well.

Hope that made sense - all I'm asking for is something like "Bangkok -> Phuket -> Koh Samui -> Koh Phi Phi -> Krabi -> Bangkok" (I just made that up). Thanks in advance!

Thank goodness you only made up your route. route Koh Samui is in the Gulf, the others on the Andaman Sea coast.
Bangkok- Phuket isnt all on the train route. You'd have to get off at Surat Thani and get a bus. Same going between the 2 coasts its either a flight or an all day bus trip.

Bus Bkk to Phuket, ferry to PP, ferry to Krabi, bus/ferry to Samui, train to Bkk from either Surat Thani or Chumphon.

See the following website for train travel In Thailand and links to islands

http://www.seat61.com/Thailand.htm

flip your trip around go from bangkok to surat thani catch the ferry to phangan, ferry from phangan to samui and then either a flight for 100 dollars to phuket or take the ferry to surat thani and bus from there.