I always c-bet this flop, b/c with the flush draw and inside straight draws on the board, checking screams "I don't have AK or AA!" I almost always bet the flop after I 3-bet pre-flop. There are some special situations where I won't (think it's likely I'll get c/r'ed, flop a huge monster, villain has a small enough stack that it will only take two streets to get it all-in are a few that come to mind).