I feed my cats Natural Balance, and I think highly of the food as a whole. It has good, high quality ingredients and seems to be quite tasty (to the cats, at least. I haven't tried it myself
With that said, my first pick for a food for a cat with a history of crystals would be EVO. I've done a good deal of reading on the subject of crystals and food, and it seems that the best choice of food would be one high in protein, low in carbs, and most importantly, canned.
Basicly, struvite crystals for when the cat's urine becomes too alkaline, and having concentrated urine further complicates the matter. Wet food is a necessity because it dilutes the urine and makes it more likely that deposits in the urine will be flushed out before they have a chance to clump together and create crystals & blockages.
Carbohydrates are shown to increase the pH of urine, making it more alkaline, where protein does the opposite, and help to create a pH in the normal range for a cat, so you will want a food with fewer carbs.