Going to an i5-2500k build, which chipset would be the best?
1) If you will use the integrated graphics, then the Z68 will be necessary to overclock the "K"
2) Video encoding is better on the Z68
3) The ssd cache on the Z68 is a marginal benefit in select configurations.
4) The Z68 will be a bit more expensive.
The Z68 is newer and has no downside, so I would consider it best, and probably worth the small price premium.