The leaves of the alfalfa is where all the nutrition is and what the chickens want to eat. A bale or loose gleaned hay is best. I had gleaned a lot of loose alfalfa hay last year and it was great to have for them.
Cubes can be crushed and fed dry, or soaked, wrung out and fed. Be aware that cubes have a lot of rough stems in them, which might be good for rumaniants like cattle, but your birds will pick through and leave them.
A bag of cubes is easy to store, I will give it that.