yes, i like mijita a lot. been there ~10-20 times over the years probably. Chilaquiles, Nachos, and Fish Tacos are the things i get there.
Roli roti porchetta sandwich during the farmer's markets is my overall favorite thing.
boulette's larder has good food, but is extremely expensive for what it is. mietta is pretty but simply not very good imho. raclette on toast on saturday mornings is a nice snack. i've had good noodles from the tea shop, but that was a long time ago (i need to try them again.) grilled cheese sandwich at hog island oyster is worth a try. so is the muffuletta at boccalone.
but in general, just walking around and trying whatever looks good is recommended.
I have enjoyed the food at Mijita. It is more pricey than your typical Mission District taqueria, but that's to be expected in the Ferry Building. They do use quality ingredients and the food has been well-prepared in my experience. Overall, it's a good place for a snack or light lunch if you are in the area.
If you are there on a market day, Tues, Thurs, or Sat, then you will have some additional choices of the vendors outside the building.
Of the permanent vendors inside the building, Il Cane Rosso, is known for good sandwiches. Gott's Roadside for various kinds of burgers. Hog Island for oysters and other seafood. None of these will be particularly inexpensive.