Chickens like oats, but remember that oats shouldn't constitute an enormous portion of their diet, like all things, moderation.
They'll eat any kind of oat you want to give them Whole, rolled, cut, quick, etc. To be affordable, rolled oats can be purchased in huge bags at the feed store. Whole oats as well. Some birds simply do not care for whole oats and may balk. They are very high in fiber. What if you've purchased an expensive bag of whole oats just to find they balk? Rolled oats will never be looked at side ways. Just sayin. I've had to use up whole oats before by soaking them for 24 hours in a feed bucket. That's too much fussing for my taste. I watch the flock. If they eat whole oats, great. If they balk, that's it, I'm done with them and I feed them to the other flock that doesn't care. Whole millet can sometimes be the same way. Even cracked corn or whole corn isn't wildly popular with some of them.
Smaller flock keepers should test the waters on some of this stuff before investing in huge bags of various things, I suspect.