I have been to a ton of taco joints in Dallas. From trendy tacos to taquierias. My favorite, close, go to tacos are from the chevron @ Greenville and Lovers. It's a pretty sketch neighborhood, so if you're a couple of girls pulling up in your mercedes, you may want to pass. The chicken (and i NEVER get chicken at a tacquieria) is so good. The rest is okay.
Tacos Al Guero over in east of Deep Ellum is also very sketch but very good. The tacos are much smaller than the chevron, but they're good. Their Suadero is excellent, I can eat about 10 of them.
As for trendy, good 2 go is unbeatable. Velvet taco moved into my neighborhood and it's really good, but good 2 go is far better. No others seem to make a mark in my head.
There is this real sketch gas station across from bachman lake that ken rathbun once posted about to go get tacos at, so I did. It's the only place I've been that serves Trompo - spiced pork on a spit. And the trompo delivers. I could drink their orange salsa.
feel free to ask me about tacos anywhere, i'll review if I've had them or I'll go eat them if I haven't - I have a taco problem.