I'm from San Diego, so I was happy to see that a Tacos El Gordo was across the street from the Encore. It was windy and very cold when we went, but we didn't care. They were so busy that there wasn't any inside seating and the lines were stupid long too. We had to eat outside, but that was complicated with not high tables or chairs out there.
The tortillas are made fresh and the guys behind the counter are fast. Some dishes take a lot of time, so I hope the person in front of you doesn't order something like mulas because it requires the melting of cheese. That could easily take up to a minute to make. Other than that, I recommend any of the tacos. I've tried a bunch of their meat, but I like the al pastor the best. I've had the quesadilla and mulas and I'll always come back just for the tacos.
For about $2.50 a taco with tax, this will be one of the best deals on the Strip.