I have fed all three of those while I don't really dislike any of them her are my thoughts:
Hubbard Breeder pellet--Birds did well on this. Couldn't get the nice glossy look I wanted for show condition, the adult Cornish got really heavy on this feed. Fertility good.
Kent Multiflock--Loved the mini-pellet, but didn't work nutritionally for a subset of my Bantam hens. Everybody else looked good, nice and glossy. Fertility good.
Purina Flock Raiser--Really wish it was a pellet. I took down all of my hanging feeders and went to trough feeders to minimize waste. Cornish gain steadily and keep good weight on this without getting fat. Fixed the bantam hens. I do suppliment with salmon/mackrel once a week. Birds look good, haven't done a hatch on Purina. I will be setting eggs in December, so we will see how that goes.
I really do like the Kent Chick feed the best, low dust, perky happy chicks, with good poos and no pastey butts--winner hands down.
Just my thoughts.