I am a big fan of Rubios. My favorite is their gourmet shrimp tacos. There are a couple coupons throughout the year which is always a nice touch. While they are usually clean, this one didn't have anyone wiping tables and it wasn't busy but they are usually good.
I love that they have 4 different types of salsa for you to try. I got a coupon for chips and guacamole which now made me hooked on the guac! Fast service and good food.
Another good choice if you are watching calories is their health mex burrito. I do add some balsamic dressing to it and it is really good for a healthier option.