Ain't it the truth. While I do like El Rey del Taco, it's not my favorite Mexican place in Montreal. La Matraca at 4607 St. Denis (above Mont-Royal) for Mexican street food, T and T Tacos and Tortas at 51 Rachel West (corner of Clark), and La Tamalera at 226 Fairmount and numbers 1, 2 and 3 in my book.
Rumples, I have tried La Matraca and I concur, it's great food and quite reasonable price wise as well. Love the pastor taco' s there. If I recall they don't accept credit-debit cards there so best to have cash readily available if you go. Haven't tried the other couple places you mentioned, but I will certainly put it on my to do list when I head back to your wonderful city.