They are the same feed. Pellet is usually a little more expensive, because it requires an additional machining operation to press the powder into pellets.
The advantage of pellets is in waste management. I'm sure you've noticed that chickens are nOT dainty eaters, food tends to get flung everywhere. Loss can be quite high, 10-15% estimates aren't uncommon. Likely much higher than that with chicks, judging by the bottom of my brooder box. Ducks even worse.
Anyhow, pelleted feed tends to stay together when chickens walk thru it, push it out of the feeder, whatever - meaning there's a decent chance that a hungry chicken wandering by later will see that pellet and eat it off the ground - while crumble tends to get scratched into the earth and mixed with sand until unrecognizable and unpalattable.
Again, many who feed crumble choose to do so as a wet mash (oatmeal like consistency) or a strained ferment (a bit soupier) to reduce waste and combat that. I personally feed crumble as a wet mash.
and if you have hatchlings, full sized pellets don't work well. That's the only situation I can think of where crumble is universally consiered the superior choice.