Bypass SF and go through Oakland. The best tacos are to be found near the Fruitvale BART station, mostly along International Blvd. There are 5 or 6 trucks and I don't recall all the names, but they are all good. In particular, don't miss the El Ojo de Agua truck on Fruitvale St, a block west of International. It's just one man's opinion, but I haven't found a single taco truck in SF that compares.
International Blvd is great for the variety, volume, quality and ability to check out a lot within a short range but the OP mentioned SF.
I second El Tonayense. It gets mentioned for a reason. I like the torta al pastor (sandwich).
Also there's Los Compadres at Spear and Folsom, closer to downtown in SOMA. I've been a couple of times and it's as good as any truck I've been to, although I don't know the consensus best item...the carnitas is v.good.
Los Compadres Taco Truck
292 Spear St, San Francisco, CA