I personally think a wider, flatter roost is more appropriate. Why? I'll give you my reasons.
Now of course, a chickens toes can drape/curl over a round roost, although maybe not neccesarily with the same force as a parrot on it's perch.
Now us parrot owners have found, through years of trial and error, that a simple dowel is not good for our bird's feet- there is a high pressure zone at the top of the perch, and the thinner the perch is, the more this pressure increases, leading to pressure sores and bumblefoot. This is why it is better to use rope and natural perches for caged birds, so they can change the way they are gripping any perch so as to not get pressure sores. Most caged birds do not spend a lot of time on the ground either, so a bunch of round dowel perches of the same diameter will lead to arthritis after a while
Many caged bird owners are coming to see the advantages that platforms have for their parrots --in the wild parrots do not sit on perches all day, they are flying, foraging, nesting... even at night it has been observed that wild parrots will go out of their way to stretch out and lay upon a secure surface -- in the wild they simply do not sit and grip a perch all day, they're flying miles and miles for search of food and mates and very little of their time is actually spent sitting around.
I now use a platform for my cockatiel, and she uses it every night in preference over her perches. My senegal parrot has a very wide round perch (so wide it is almost flat for her) to use to sleep on, and she does. My sun conure and lovebird both have their respective sleeping pouches, and they use these without fail.
I think in general, a chicken being a much larger, heavier bird, that they would prefer flatter spaces to roost upon. They'll be steadier, and their feet will be less prone to injury.
Each to his/her own, but thats the way I see it! I use 2x4s with the wide side facing up for my birds... but I wouldn't hesitate to use very large, thick branches either... but they would have to be at least 8-10'' around.