It depends on the stakes you're playing, really. If you play a small stake game with a lot of fish you'll get paid off more often. It also depends if you raise pre-flop, because if you do then you'll go heads up or three-way, and if you hit there's less of a shot that they'll get cracked. On the contrary, if you limp in and the pot is unraised a lot of hands that wouldn't normally be in now can flop something like a fluke straight or at least a draw to one. You'll get paid off more by limping but you will get cracked from time to time. I usually will make a small raise with a PP, just to attempt to get the blinds to fold their hands.