I'm a big fan of rings, and i just bought randomly off ebay. I'm just about to go there again and buy another lot soon too.
I bought in 2 or 3 lots, a few each time to combine postage, and i ended up with:
S&W - a bit more expensive than the cheapest, but i bought them all from one guy and paid the same postage as one ring, so ended out cheaper all up. The best thing about them is they come with a nice soft plastic pouch-envelope thing (i know i'm not describing it the best, want a photo?) that i've ended up using to keep my filters and pinholes in.
Sonia? i think it says - the step down on these are cut all along the sides vertically for extra grip, the step up have a diagonal bit chamfered off the top for grip. all my other brands are silky smooth on the outside, so less grip to get them apart (by the same token: less grip to force them stuck together). came in a throwaway paper box, so now jangle loose in my bag (but mostly i keep them stored on lenses or together in a stack anyway).
Kood - think it was more expensive again, only got one, but it was the only brand that made a certain size i wanted.
noname brand - no idea, was dirt cheap and chinese i think. still, nothing wrong with it.
all of them together, i've never had a problem. Even if i thought in the past i've stuck them irreversibly together, the next time i try they just come apart. each brand to each other or between brands.
no brand can shield you from that 100%, but taking care of them will. never force anything, stop and take a deep breath before you break anything.
There are differences between brass/aluminium/steel, but you never know what you're getting even if they do state it on their ad, i can't remember which one is meant to be better anyway. just make sure they're black, i've seen steel-polished ones and that's just asking for ghosting...