The XFX appears to have the wrong description for some reason, but the part number and price seem right. Probably just a typo, someone copying and pasting the wrong description.
The XFX has a lifetime warranty, the Diamond has a 5 year (wow, when did they change that?) and the Powercolor a 2 year.
I've not had to RMA anything to any of those brands, and haven't owned a card by them. When I was building day in/day out, we used a lot of XFX cards, had a few problems but nothing major. We didn't use Diamond at all, they're not big over here, and we only used a few Powercolor because again they're not that common and if I remember correctly they're part of another company whose cards we may have used instead.
I would say it's pretty much a wash, if the lifetime warranty appeals grab the XFX, the Powercolor is cheapest and if the MIR works out it'll only be $80 which is pretty good. The cooler on the Diamond looks a bit dodgy, but to be fair they're all non reference and won't cool as well as a standard card so again probably a wash.