Great bang for buck. If you're craving some Mexican to fill you up for ~$6-7, this is the place! It's very customizable and there's a lot of options to choose from - the ingredients are very fresh. You can tick all the options you like but it seems like most people like "everything" on it! I find it amazing that they are able to stuff all the ingredients in one burrito!
I think the most popular choice is chicken, and I'd stick with all their sauces and choosing everything on it (except for the odd things you don't like eg. hot peppers for me). Make sure you go hungry - you'll be bloated after!