My two cents as someone who lives in Mexico:
Authentic Mexican is a funny word. Like in the US, there are tremendous regional variations in how food is prepared. And, being a matter of taste, people like different variations according to their own opinions. That being the case, there doesn't seem to be much value in debating weather central mexican, northern mexican, tex-mex, new mexican mex or irish mex is the most authentic. I like the guys response that said that he likes to find the local mexican wherever in the world he happens to be. That sounds fun.
For me, my current favorite flavor happens to be produced in Mexico. There is a roadside pollo asado stand a couple miles from the airport and my buddy and I stop there regularly for a chicken and beers after we fly. Last time it was $7 total for the both of us. "El mejor pollo, el mejor clientes" is painted on their wall. I agree!
Edit: I just noticed someone else drew the distinction between different regions in Mexico. So, yes, he's right.
