Corsair.
First, it's all about the performance and 2nd all about performance per dollar. I avoid "off brands" for reliability, tech support and customer service issues. Most of my builds include either Mushkin or Corsair. I used to use more GSkill "back in the day" but ...
1) I have had more RMA's w/ GSkill (5) than all others combined
2) I never seem to have luck marrying two Gskill's w/ 2 other modules of the same spec by another brand whereas Corsair, Crucial, Kingston and Mushkin all seem to play nice together.
3) have had more than one unpleasant experience with GSkill's customer support.
There's a lot of misinformation out there about RAM.
1. Faster RAM has no impact on gaming performance ........
http://www.anandtech.com/show/2792/12
22.3 % (SLI) increase in minimum frame rates w/ CAS6 instead of CAS8 in Far Cry 2
18% (single card) / 5% (SLI) increase in minimum frame rates w/ CAS6 instead of CAS8 in Dawn of War
15% (single card) / 5% (SLI) increase in minimum frame rates w/ CAS6 instead of CAS8 in World in Conflict
Also see
http://www.bit-tech.net/hardware/memory/2011/01/11/the-best-memory-for-sandy-bridge/1
which shows only 1 fps .... but that's a 5% increase. Is it worth it to pay 20% more (say $60 versus $50) for faster RAM to get a 5% performance increase ? If ya look at it that way no...... but if ya consider that your $2,000 system in its entirety got 5% faster ..... then that's a 0.5% increase in system cost for a 5.0% increase in speed, then the answer would be yes.