I like to offer two roosts usually of differing heights and let the chickens figure out their happy spot. If the coop is tight though, make sure you even have room for the 2 roosts you are mentioning because the birds need to be able to hop/jump/fly to get on them. The tiered setup also allows them to hop from the low to the high instead of trying to jump the entire distance to the high. And all that said, make sure you get them up higher than anything you don't want them sleeping in like nest boxes. If they feel like they're up as high as the roost, then they thing they're roosting!
