Finally got around to trying the El Chato taco truck parked on Olympic and La Brea. I found the lengua and al pastor to be above average. One reason may be the good amount of lard they use on the grilltop. I watched as the lady warming the tortillas dip a stack of tortillas in the warming pan of lard and dripping a lot of it over the tortillas on the grill. Nice touch. I also like the grilled onions they include on the plate as well as the onion/habanero slaw they have out for spicing up the tacos. All in all, it's a very satisfying place.
There's now a taco stand near the corner of Pico and Arlington in front of the church there. When no one's around, it can be a lonely stretch around there, but there seem to be a steady stream of people coming and going. Most noticeable is the al pastor spit, and they have the flat grill as well as the well of meat juices in the round grill with cooking meat along the edges (forgot what that's called). The al pastor was above average, but the better filling for me was the cabeza. I found this stand to be the equal of El Chato, and I like that all the sauces/salsas/garnishes are on the table for customizing your way. Really nice folks running the stand. I hope they stick around.
When I was a kid, I used to eat at the Pup 'n Tacos on Pico near Queen Anne Place/West Blvd, so I knew I had to visit Tacos El Compita which moved in to the remains of that forgotten fast food location. (I've already posted elsewhere about the first KFC I tried that is now the Oaxacan restaurant Zapoteca on Pico near Crenshaw, and Tasty Q, which is in the first Taco Bell I ever had). The cabeza and lengua are two of the better options there. Avoid the al pastor. I ordered a lengua burrito, and the counter guy took out a large lobe of tongue stewing in the steam table, peeled the membrane around it, and chopped it up and straight into the burrito. Worth every bit of the $4.50 they charge for a burrito. The cabeza is also kept warm and stewing in a steam table pan, and the flavors of the headmeat melds nicely into a tender hash.
While none of the places above push the envelope of taco making, they're all solid, and will likely satisfy in the neighborhood. If I had to choose the place that will draw me back among the three, it's probably the stand at Pico/Arlington.