Which will be the best graphics card for my Build?

Either you spend a little bit more and get the GTX670 or get the HD7950 which is probably the best performing card at less than $350.

By the way, what psu is that? Just knowing it's a "600W" unit doesn't really tell much. You wouldn't want to put a high-end video card on a cheap, poorly build power supply.

I would go for AMD 7850 since i don't care playing in highest settings and save some money for the next upgrade..
But you need to tell us more about that 600w psu

For the money, the 7870 LE (also called the 7870 XT) or the 7950 is your best bet. Both have excellent performance at 1080 and fit your budget. I feel that Nvidia's 660ti and 670 are both overpriced at their level of performance. Here's a nice resource if you haven't already seen it: http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html

I wouldn't use a generic PSU with such a nice system, I'd buy a branded PSU from a reputable brand (Antec, Corsair, Seasonic, to name a few). Don't forget a cooler for your 3570k unless you aren't overclocking and are willing to use the adequate but inferior stock cooler.

Assuming that you have an acceptable power supply (you did not state any specifics besides maximum wattage) - Go for the 670 if you can stretch. If not, I would probably consider a 660 TI or an HD 7950. I personally prefer the 7950 simply because the HD 7950 has a 384-bit memory interface and the 660 TI only has a 128-bit interface.

A little correction, the 660ti has a 192-bit memory bus. But yeah, I prefer the 7950 over the 660ti as well.

It's 192-bit, but your conclusion is still correct.

If you only go by benchmarks your missing a BIG part of the equation. There is hardly any difference between a 670 and a 7950. I know Tom's does recommend the 670ftw over the 7950 though. I think they do on their "Best GFX for the Money of March". And I think it also has a higher percentage of performance in the Tom's Hardware article.

IMO, if you go with Nvidia you get the highest quality. Did you read the review comparing two 660Ti's in SLI vs. two 7870's in Crossfire? Of course the 660Ti "wins" but that's not the point of this review. Tom's did a review showing which cards in SLI/Crossfire produced the most runt/dropped frames(or frames that don't affect what you see on the screen positively). And the 660Ti mostly didn't produce ANY runt/dropped frames while the 7870 produced quite a bit. Which actually means, with AMD cards, fraps might say your getting 100FPS, but actually your getting 95FPS. So if you take that in to account the 7870 was even further behind. If you look at the graphs in the review, the 660Ti's graph looks perfectly in sync while the AMD 7870's graph was jumping up and down. And this was with almost every game they tested with.

This only further proves to me that what you get with Nvidia, is HIGH quality. Nvidia has the money to make sure everything is picture perfect with their hardware. I'm not saying AMD isn't quality, but clearly they are behind in this respect.

Plus, if you game in 3D, like me, Nvidia is a must. Not only is their 3D tech the best, but it's supported by almost every monitor while AMD's 3D is not. Like my BenQ 2420TX 3D gaming monitor supports Nvidia 3D Vision 2 w/light boost and you can't have an AMD card if you want to play in 3D. I also highly recommend 3D as now every game comes in 3D. Not only is it beautiful, but your FPS doesn't take a hit much, and 3D monitors don't cost much more than normal monitors. So why not get you some 3D? In which you'll almost need an Nvidia card.

Nvidia also has PhysX. Which is some really cool looking effects in quite a few games, like Borderlands 2 and Batman: Arkum City. Granted, not too many games have this, but for my Batman and Borderlands 2 games I couldn't go without it.

Nvidia also gives driver updates as new games come out. I got my system late December 2012, and it's only March and I've already had to update my card 3 times. So you know their on top of it.

So yeah, I'd recommend the 670ftw because of it's price/performance/quality/3D over other competing parts.

And I'm not biased either, I just bought my little brother a 7870LE Powercolor Myst Edition with the Tahiti GPU. It was only 239.99 and came with Bioshock Infinate and Tomb Raider. He was going to get Bioshock anyways. Now this card does draw lots of power, it's loud, isn't as high in quality as far as build goes, and it runs hot, but it performs almost on par with my 660Ti, it was cheap, and my brother doesn't have a 3D monitor. So people choose what right for them.