LTU has a good bartender. Same with Pushcart. Omar at Xtabi is great. DJ at Kuyaba knows what he is doing as well. Most of the more "upscale" bars/restaurants have very good bartenders. Almost all the bars have a wide liquor selection, so crafting a special cocktail shouldn't be a problem. Try the frozen drinks in Negril, such as the Dirty Banana or Hummingbird....