I actually have one Feisty ferret home, and one ferret nation for my chins. The feisty ferret is actually not a bad cage, and has actually worked rather well for us. You will have some problems if you use bedding, and will have to buy or make some sort of pan for inside it. I use liners so I don't have that problem. Only one door on the top, and one on the bottom opens, so that can be a pain sometimes, but still works.
We actually just got our ferret nation and love that cage. It is alot bigger and stronger. Same thing about the bedding. Both doors open, which is nice.
So generally. If I were to invest the money in a brand new cage, I would go with a ferret nation. If however someone offered me a feisty ferret, or it was on sale, I would probably buy another one of those down the road as well.