I don't use either, I like using crumbles. My chickens have always done great on it. I have it in a hanging feeder and the only time that I see any wasted at all is when I spill it myself.
with pellets, each bite they get a complete ration. With mash, they can sort out, altho studies show, given a chance animals will eat a balanced diet (unlike humans).
From a digestability standpoint, pellets digest better (way they are made) than mash.
Crumbles are pellets that have been smashed into smaller parts.
Ya get less wast with pellets an it works in more feeders. I'm feeding mash now couse I'm getting a deal in it. (commercial egg farm feed) But it packs an clogs in the feeders especially when the humidity is high. It also don't work well tossed on the ground or in there bedding. I say if price is the same I would only use pellets.