What is the oldest -- and presumably best, since it's been there longest -- Mexican restaurant in Las Vegas?
We still mourn the death of El Sombrero on Main Street downtown, which operated in the same location and under the same owner family from 1950, in a building that went up in 1935, through 2014. The Sombrero's huevos rancheros were second to none.
Beyond that, El Torito Cafe, at 2126 S Boulder Highway in Henderson (not to be confused with El Torito Mexican Restaurants, with a couple of dozen locations in southern California and four in northern California), opened in 1975. That makes it the oldest Mexican restaurant not only in southern Nevada, but in all of Nevada.
It's a fairly long low-rise building on Boulder Highway just north of the intersection with Interstate 11. It's open Tuesday through Sunday 10 a.m. to 8 p.m. and has been in the same family for all 45 years of its existence, as have the recipes on the extensive, though typical Tex-Mex, menu.
We've driven by the place countless times, but admit we've never eaten there. However, we will, now that we've looked into it and realize that we should review it.
On the other hand, the question asks about Las Vegas specifically and we can say that we've eaten more times than we can remember at Dona Maria's Tamales, first in its original location on E. Charleston that opened in 1980 (making it, as far as we know, the second oldest Mexican restaurant in Vegas proper) and its current location on Las Vegas Blvd. just north of Charleston, where it moved in 1990. In 1998, Dona Maria's opened a second location in the northwest valley on N. Tenaya near Cheyenne.
Dona Maria's is the place to go if you want the best downhome tamales in the state, which come in pork, chicken, cheese, and beef (and a sweet dessert tamale with raisins and pineapple). With the free chips and salsa, a single a la carte tamale has always filled us up and when we first started going there in the '80s, we were out the door for $3, including tax and tip. Now it's more like $6, but still as good as ever.