You can't compare Del Taco to Chipotle, that's like comparing McDonald's to In n Out; they're on different tiers.
Chipotle is comparable to Qdoba or Freebirds. Personally, I think Chipotle is slightly better than Qdoba and a decent bit better than Freebirds.
Del Taco is comparable to Taco Bell or Taco Johns. Personally, I think Del Taco is infinitely better than Taco Bell.
Some pointers for Del Taco:
Don't waste your time getting the burgers or "American" food, that's like going to Carl's Jr and ordering the Green Burrito shit
Their fries are pretty decent, better than a lot of fast food burger joints
The chili cheese fries are usually pretty damn good though occasionally I get some that suck hardcore for whatever reason
If you're ordering generic tacos y burritos expect cost and quality on par with Taco Bell
Getting into the more "exotic" menu items at Del Taco gets you the good stuff
Chicken soft tacos are really good and a screaming deal, though the chicken seasoning makes everyone I know have some really raunchy burps
The Del Carbon tacos are actually a decent facsimile of a true Mexican street taco. They're a bit pricey but maybe my favorite thing on the menu
I would (and have) ordered fish and shrimp tacos from Del Taco, something I would NEVER do at Taco Bell. Again, they're pricey but I was not disappointed
The quesadillas at Del Taco are literally 10000000000000x's better than Taco Bell. You can get cheddar or spicy jack varieties and they're actually made (i.e., put together) there. Taco Bell quesadillas are shipped frozen and reheated whole, often meaning that they're not properly warmed through.
In fact, it's been said that Taco Bell really took off in this country when the company realized that it doesn't compete against restaurants (which implies cooking food) but instead competes against cafeterias (which only reheat already prepared food). I would agree with this wholeheartedly and state that while Del Taco is certainly not haute cuisine it is light years better than crud like Taco Bell.
Taco Bell : McDonalds :: Del Taco : Wendys :: Chipotle : In n Out
There's definitely some quality stratification going on.