Both are fine. This is actually the Worrall Variation of the Ruy Lopez. There are many available options for black.
both good... they are two ways to do it but a6 said to the bishop that he has to do something
Okay, so 4 ... a6 is an attempt to transpose from the Berlin Defense into the Ruy Lopez, Worrall Attack (C86) 1 e4 e5 2 Nf3 Nc6 3 Bb5 a6 4 Ba4 Nf6 5 O-O Be7 6 Qe2.