I took my daughter to Guanajuato when she was in college minoring in Spanish. She had taken a lot of classes but never spoken with a native. The first morning we were in the hotel restaurant and the waiter asked, "Le gustaría algún café?" (would you like some coffee). She replied, "Sure!". Fortunately her Spanish improved by the end of the trip.
I like Guanajuato because, although it's geared towards tourists, it's not overrun with gringos. San Miguel has that covered. Guanajuato caters more towards Mexican tourists.
There's a Rally Car race every Spring that starts in Guanajuato then moves out into the mountains. The start is a night circuit inside the city. Several of my coworkers from our plant in Reynosa go every year and it's been on my bucket list but I just haven't been able to make it happen yet.