Petroff with 3.Bc4

Right now I just play 3...Nxe4

What should I play after 4.Qe2 or 4.Nxe5? 

d5 looks good.

3..d5 blunders a pawn i think. exd5 nxd5 Nxe5 Qe7 O-O, no easy way to recollect it, perhaps a gambit is in need here.

3..d5 4.exd5 e4 5.Qe2, and play from here is probably better for white, its not immediately clear how black will justify the pawn sacrifice.

Think the OP asked about move 4, where he always plays Nxe4 on move 3.

3...Nxe4 is the Urusov gambit I think. Taking is theoretically best but you're probably going to be defending until move 20 something...

No, it isn't. The Urusoff goes 1.e4 e5 2.Bc4 Nf6 3.d4 ed4 4.Nf3.

Anyway, 3...Nxe4 is best, and absolutely safe for Black, no long defence required. White may try 4.Nc3, when Black can pick between the old equalizer 4...Nc6, or 4...Nxc3 5.dc3 and now 5...c6 is safe and clean equality, and 5...f6!? goes for the win at some risk.

And of course 4.Nc3 is a better move than 4.Nxe5? and 4.Qe2?! which are both perfectly well answered by 4...d5.