Encouraged by posts here, tried Tortacos last week. The reviews are accurate -- family-run; very fresh; everything well above-average for these parts. Limited menu, but they're focused on what they do well. Revisited Taco Bar (gas station, Gaithersburg) this weekend for comparison. Much busier than Tortaco -- indeed, much busier than I've ever seen it. I love the posole at Taco Bar, which is reason enough to stop by frequently. But the tacos were very good, too. Only item I had in common with my order at Tortacos was a sope al pastor. Fine rendition at both places; slight edge to Tortacos, where the flavors were more distinct.
P.S. Not that it's in MC, but R&R Taqueria, in a gas station in Elkridge, is indeed very good, although perhaps not quite the nirvana that Todd Kliman and Tyler Cowen describe.
All three of these places are well worth your patronage.
9629 Lost Knife Rd, Gaithersburg, MD 20877