Crumble is a bit more expensive, and much more wasteful. Occasionally, a flock will resist the switch to pellets. But, if they are hungry, they'll eat what ever is set before them. PP have mentioned tossing a few pellets on the ground when first introducing them. Chickens are competitive enough, that they will gobble up such things just to keep a flock mate from getting them. Once they are over the freak out about "something new and scary", they will do fine with them.
I ferment, so the "shape of the dry product" does not matter to me, unless I'm feeding dry in a deep freeze. The cheapest form of feed is mash, if you can even get it, but I'd never feed that dry.