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.