I have had Tex Mex, as well as Arizona style, but I think SoCal authentic places have better flavors and ingredients.
As to the difference, between “Americanized” and authentic Mexican...you don’t get much more authentic than eating in East LA.
I’ve been to Mexico, but prefer their food up here in the states better.
Even though I haven't sampled enough Mexican food in Texas to rate myself as any sort of expert, I have a feeling that that's true. I just don't see lot of Americans frequenting the Mexican food establishments here, which tells me all I need to know. In L.A., you always saw more gringos in the Mexican restaurants than Mexicans.
Don't remind me about East L.A. I get hungry just thinking about it. Do you know, we don't even have Mexican roach coaches out here?