You don't want to read 300 pages of posts to get that?
[disclaimer - me not expert. just feed chicken and read long fermented thread]
Any grains / crumble / pellets / mash can be fermented. Most people on this forum do a mix of grains with a prepared poultry feed (i.e. mash) since grains alone does not provide ideal nutrient levels.
Deciding what to ferment is not really the right question. You should decide what you want to feed your chickens (in general) then ferment it. There's lots of resources about that...
My current fermented feed is a mix of 1/2 18% poultry stater mash and and 1/2 hen scratch which consists of whole wheat, whole oats and field fields. Everyone does something a little different. Some use barley cause it's cheap. There have been some unfavourable studies about the use of barley in the poultry industry but the backyard chicken folks seem to be having success with it.
My preference is to NOT to use cracked, cut or rolled, or otherwise processed grains because as soon as you process the grain in any way it starts to degrade. I use the starter mash for convenience to get the missing nutrients and keep the protein percentage acceptable.