Both are not that very good for bichirs if it becomes the main diet. I noticed that they get bloated easily with those diet. As everybody would agree, variety of diet is always good.
My main staple for my polys were pellets (carnivore and cichlid gold) then I threw in some tilapia and shrimp with mysis shrimp and black worms on various days of the week
I just like to mix it all up, theyve even eatten NLS Thera - A