never buy a sparkle , well at least a sparkle graphics card.. their psu's are alright
as for ati vs nvidia in the gtx 460 range assuming 1 gig the competition is a hd 6850 they are close enough that without knowing what games you play i'd toss it up to which you can get for a better price
If your motherboard is crossfire grab ATI. If it's SLI grab nVidia. If it's neither grab whichever one you want. Their performance is quite identical, however depending on the games you play we can recommend the one more suited for you.