I would say either Wakatobi or Malapascua in the Philippines, depending if you want more quiet. Malapascua is mellow with a couple bars and actually good food but not much else to do but dive and chill. I was there for three weeks this summer and it's pretty amazing. I saw Mantas, Thresher sharks, sea moths, white tips, these really cool sea cucumbers that look like soft coral or sponges eating (it's cooler than it sounds) loads of juvenile sweet lips and pygmy sea horses. I fell in love with the place, and I think it's less pricey than most places. Envious!!