Depends on what you want. If it's beaches, good food, exploration you went, Thailand. Hands down, motherfucking Thailand (and it's not just cause i've recently been.) Thailand was the shit and there are cool as fuck people everywhere you go, and not just Americans--(i assume you're American working in England like FC?). I barely met any Americans at all when I was there, and it was a perfect mix of people from all over the world, esp. in Bangkok.
Bangkok you have the city experience, with badass temples and palaces peppered throughout.
Up north you have awesome, chilled out mountain towns. Weed, while still highly illegal, is super fucking easy to get up here. I would highly recommend
Pai -- It was my favorite place on the trip.
But if it's beaches you want, fly into Bangkok and head south. There are shitloads of islands and beach towns in the south -- Phuket (touristy), Krabi, and the island Koh Phi Phi (good for diving I think) are all very popular. Those are on the west coast, and I didn't get a chance to go them--will try again next year. East coast, Koh Samui, Phangan, Koh Tao, are all also great. If you are in Thailand during a
Full Moon Party, I would highly suggest checking it out. Tons of drugs and hot women, and mushroom shakes. Ko Tao has really good diving too I guess.
While i'm very partial to the northern mountainous areas, I can definitely see the appeal the southern beachy areas have for a lot of people. You could definitely do either the east coast or west coast (choose one) in one week, or both in two weeks, but you'd constantly be on the move every couple days. If you only have a week, i'd recommend Bangkok for a night or two, then the East coast island hopping trip. Or, if you're strapped for time, you can get a connecting flight (enter and departure) from Bangkok to Surat Thani, which is right down by the southeast Islands.
EDIT: Also apparently it's super fucking easy to hook up in Thailand but as i've already said I have the worst luck in the world with that. If you do go to Bangkok area, I have tons of friends I could hook you up for couchsurfing so you could stay for free. There is this one place, called N6, run by two Thai/American women who live there but consistently host couchsurfers, but it's a great community house for travelers. Like a more personal hostel, I guess. If you decide to go, lemme know.