I've found that most fish come with some preferences on food, likely based on what they are used to. Most will eventually try a new food if it's all that's offered, and learn to thrive on it.
I actually got my betta some special "betta pellets" only to find that he preferred general-purpose tropical flake food. The betta pellets ended up going in the big tank, where the 'bows loved them. Betta is thriving on the flake food.
I do occasionally indulge both tanks with some frozen blood worms, which the fish love (but strictly speaking don't require.) Oddly, none seem very interested in frozen brine shrimp. I add algae wafers to the big tank for the ottos and ancistrus and occasionally a wafer or blanched sweet potato. The latter is probably more than just a treat; it's a good idea to be sure they're all getting enough to eat.