Buffalo = highly questionable quality
Corsair = proven quality
Buffalo w/Winbond has the POTENTIAL to overclock higher. Don't expect any miracle speeds though. Your best bet is to buy the fastest RAM you can.
I have several (6+ now I think) sticks of Buffalo pc3200. It was a complete nightmare getting them setup...I had 4 bad sticks out of 6. Newegg was great about replacing them, but it still was a hassle. Took a month before I finally had 6 good, working sticks. Now, that certainly may not be the norm...maybe I just got sticks out of a bad lot. But, because of that, I won't buy Buffalo sticks again and I can't recommend them to others.