Best places to visit in Thailand on a 2 week holiday?

I am going to Bangkok for 2 days then Koh Samui for the rest. I am going for 2 weeks this Thursday!

Bangkok for three days only, then an Island. My favourite is Ko Samet.

Bangkok - Phuket - Koh Samui.

Well I'm going to Phuket and Bangkok for my honeymoon.

Bangkok and Ko Pan Nagn