I actually just posted a question on another forum comparing Mazuri and Kaytee Forti-Diet. Looking over the two ingredients, I really have a hard time considering Mazuri something that is even suitable for our rats to be eating (however there are still plenty of people who swear by it, and have used it with good results with many many rats):
(bolded parts to show differences, and placement in ingredients list, as first in the list means it has more of a particular ingredient):
Kaytee Forti-Diet
Ingredients
Ground Yellow Corn, Dehulled Soybean Meal, Ground Wheat, Ground Oats, Ground Peanuts, Dehydrated Alfalfa Meal, Corn Gluten Meal, Dried Cane Molasses, Lignin Sulfonate, Fish Meal, Corn Sugar, Calcium Carbonate, Salt, Dicalcium Phosphate, Animal Fat, Brewers Dried Yeast, Dried Beet Pulp, DL-Methionine, Choline Chloride, Riboflavin, Ferrous Carbonate, Vitamin E, Vitamin B12, Manganous Oxide, Ethoxyquin, L-Lysine, Zinc Oxide, Niacin, Menadione Sodium Bisulfite Complex, Vitamin A, Calcium Pantothena
Mazuri
Ingredients
Dehulled soybean meal, ground corn, ground wheat, wheat middlings, animal fat preserved with BHA, cane molasses, fish meal, ground oats, porcine meat meal, dehydrated alfalfa meal, dried beet pulp, wheat germ, brewers dried yeast, calcium carbonate, dried whey, salt, calcium propionate (a preservative), dicalcium phosphate, ground soybean hulls, menadione dimethylpyrimidinol bisulfite (source of vitamin K), choline chloride, dried yucca shidigera extract, corn gluten meal, DL-methionine, cholecalciferol (source of vitamin D3 ), vitamin A acetate, pyridoxine hydrochloride, d-alpha tocopheryl acetate (source of natural vitamin E), soybean oil, thiamin mononitrate, folic acid, nicotinic acid, calcium pantothenate, riboflavin, cyanocobalamin (source of vitamin B12 ), manganous oxide, zinc oxide, ferrous carbonate, copper sulfate, zinc sulfate, calcium iodate, cobalt carbonate.
The primary ingredients for both of them are essentially all the things that are bad to see in dog food (I understand that rats and dogs are different, however fillers, fillers, horrible preservatives, and more fillers aren't good for any animal). Kaytee contains Ethoxyquin, which we all know is a bad preservative, however Mazuri also has BHA, which is a preservative that may also cause problems with rats. I'm not sure why cane molasses is even in there, except possibly to add flavor and calories.
From talking to other people about this topic, it's generally accepted that Harlan-Teklad and Oxbow Regal Rat compete for the 'top spot' as far as rat food is concerned, except that many rats end up rejecting Oxbow, to the point where they will lose weight while on it. You may be able to find a rescue or breeder in your area that distributes HT.
I know that some people don't like the idea of Suebee's diet because you have to be careful that your rat is getting everything it needs in it's diet, but if the only other options are Kaytee or Mazuri, I opt for Suebee's. I feed this with Natural Balance Low Calorie dog food (all natural, good ingredients, low protein, low fat, and no dangerous preservatives). Dog food is regulated by the FDA - small animal foods and treats sold in pet stores are NOT, so there is a lot of leeway for companies to produce items that are dangerous for our pets.