This is only my opinion mind you but the only food my bettas will eat is the HBH Betta Bites & Betta Treat. I've tried flakes (that had brine shrimp in it) but Raspy had a lot of constipation issues with that and Lilex wouldn't eat the flakes at all. I haven't tried bloodworms as of yet.
I have used the HikarI Betta Bio-Gold pellets for the whole time I have owned Bettas, but I did not vote for them as I have a new favorite food for them and they love it. It is the Atison's Betta Pro by Ocean Nutrition. When I can find a food that 5 out of my 6 Bettas eat willingly and love, I have to say that it deserves my vote. It will never be 6 out of 6 because Marty would not put a pellet in his mouth if it killed him. (He strictly eats bloodworms - nothing else)
That's cool. I have tried several different kinds of food and really this is the only one that has stuck. The other foods they've just refused to eat. I have not though tried the ones that Chickadee mentioned. Perhaps those would work too. At least it gives me an option in case one day these guys decided they don't like the HBH anymore!
Rusty prefers any pellets but mostly Topfin Betta Food, which is fairly small and which he eats as greedily as a kid eats candy. I have not yet had a betta that would eat flakes but I have to admit to being curious about whether he would or not.
My two bettas eat the bio gold pellets and flakes TenshI (female) eats like there is no tomorrow, but InarI (male) is a bit more picky about what he puts in his mouth and if he is even hungary he has spit pellets back at me for no apparent reason then TenshI eats them I don't understand it but hey what every floats their boat I guess.
If you can get your betta to eat more than one food, that would be ideal. Variety is the key if you can get them to eat other foods. Even my carnovore fish get veggies once a week. This will keep them balanced. My bettas always tried whatever I fed them, so I guess I've been lucky. I think Chickadee is right about bettas and flakes, but my bettas always ate them. I've also dropped those algae wafers in the bottom of the tank for my other fish (I like keeping bettas in community tanks), and I've seen the bettas peck at these too. So when you do get a betta, try to get them from the beginning to eat a variety of foods and see what works. I prefer the Omega One brand of foods, but Rose said her bettas did not like the size of the pellets and would not eat them.