I started using FDK when I saw a big can of it under a tank in one of Guapote Mel's videos. He seems to feed lots of it judging by the size of the cans he buys, so I think it's pretty good. Not real scientific, but that's what I"m going with. I buy the big Tetra cans from Amazon. I also have bought the Antarctic Superba Krill freeze dried from Ken's fish food, and from Jehmco. That stuff is very high quality, pungent, slightly oily, gotta be good for fish. I just go with freeze dried, I hate frozen foods.
I feed NLS every day or two, and FDK 1-2 times a week. And since I have Vieja, I put a zucchini or romaine lettuce in the tank every couple weeks, too. Reading what RD says, I'm about to get some unsalted kelp from the chinese grocery, or nori seaweed, but I digress...