Captain America vs. Batman:
It would be a cool fight, and I would like Captain America to win. I think Batman is cooler than him, but still, it would just be unrealistic otherwise. Their fight would be cool.
Silver Surfer vs. Flash:
It would be a very complexe fight. Would Flash be able to damage Silver Surfer? Would Silver Surfer be able to hit Flash? If handled properly, this battle could be interesting. It should show both of them using their abilities to their fullest, manga style.
That's basically the only two matches which would truely interest me, lol. All around, the difference in power among DC and Marvel heroes are too big, with Marvel mostly consisting of street fighters, as opposed to DC's cosmic lightspeed fighters.