I don't have a corner cage and I don't like them... only one I'd recommend is one with more square like features than round ones.
Round corner cages can be difficult to place perches and dishes in.
The squared ones (like Fargo's cage) are easier to place perches and dishes in.
Some corner cages have "V" shaped bars. These can be extremely dangerous to a birds' appendages or even head/neck.
Corner cages really only fit inside the corner. Regular square or rectangular cages can go anywhere without looking out of place!
Corner cages have two trays and two grates. Non-corner cages typically only have one of both (unless you get double cages) - so this means more cleaning in corner cages.
Corner cages often have a bar for the double trays/grates, so yet again, more cleaning.
If you don't mind all that extra cleaning, and you get the *right* corner cages, I feel as if they can make excellent cages!