Which one of these 6600k should i get?

Solution
2 of them should be same, but on one of them on the box it says just 6600 not K. So you are stuck between box and tray. Difference is box comes with 3 years of warranty, tray comes with 1 year.
Well 1st and 3rd look to be boxed retail units. The 3rd might have a fan included, seems to be a bigger box. The 2nd one is from a tray (bulk purchase) so its just the chip and nothing else, not even a nice box.

Other than that they appear to be the same model chip so there should be no performance difference.