If a game is listed as playable on rpcs3 the game is pretty flawless to emulate. But, some games like mgs4 and infamous series are buggy and don't have good performance, so that's when I turn to the actual hardware.
The thing with the PS3 though is most games don't even get good performance on the original hardware. With the speed at which PS3 emulation is improving I've no doubt it will be THE way to play all PS3 games fairly soon.