I'm in the camp that feeds no more than once a day, or less, depending. Fry need more frequent feedings to develop properly, but once that stage is past, feedings can be less often. I do prepared foods once a day, missing the water change day and usually one other day. On the water change day, fish should not be fed prior to a disturbance so I do the change at the beginning of their day, and a couple hours afterwards they are given their weekly treat of frozen foods (daphnia and bloodworms). So that means one feeding a day, missing one day, in every 7. But many feed alternate days regularly and there is often nothing wrong in that.
With respect to the types, I do alternate the prepared foods. Currently I am feeding two flake foods and one micro pellet (for upper fish) and three sinking foods for substrate feeders. I alternate daily, so the same food is not offered two days running. I do notice a clear preference among fish, but having said that, I suspect if I stayed with only one food, all of them would in time eat it...or starve.
The nutritional value of prepared foods is quite good these days, though some are said to be better than others. I only use New Life Spectrum and Omega One. One of the three is vegetarian-based; Omega One Veggie Flakes and their Veggie Rounds (sinking). I do think it is important to get the vegetable matter in the fish, even those that are not primarily vegetarian.
Back to the frequency, it is important not to overfeed fish. A hungry fish is a healthy fish. This applies to the number of feedings as well as the quantity at each.
Byron.