Need help choosing a GFX card

[DemonicGoldfish]

Hey all. As some of you may remember, I will soon be building my first PC. I have narrowed it all down to a pretty good setup, but now I need help choosing between these two GFX cards - a Radeon and a Nvidia. The nvidia has lower memory speed and GPU clock speed (but by only a few MHz) but is newer and has more pixel pipelines. The Radeon is 2 generations behind the Nvidia, but has a slightlly higher memory and GPU speed, while having fewer pipelines but being cheaper.

Firstly, what exactly are pixel pipelines?

Secondly, which one should I get? I was thinking of the Nvidia as it will probably run with newer games (I realize that they both run with nowadays games, I'm just thinking of the future :P)

SLI compatibility is not really an issue, as it isn't within my price range to buy 2 GFX cards, and my chosen motherboard isn't SLI compatible.

So... please help :)