I also have a variety of perch sizes and types for my linnies. They do like the really small diameter (as in to me it looks like a stick) branches to hang onto and flap their wings. At my mid and lower level, the perches are mostly placed on the two shorter sides, leaving the center width open for flying back and forth, which they do. Up high I have some perches on the front as well as the sides, and I put the majority of hanging toys up there. They climb from toy to toy like monkeys and poop on them less
I have one Curly-Q toy stretched diagonally along the back wall from lower to upper, and they use it like a ladder.