Samsung will have roughly the same CPU speed, but a much better GPU. The camera will shoot 720p, the N1 only shoots 720p via a recent hack. What really matters is the compression anyway, the 720p off my EVO doesn't look any better than VGA video off my iPhone 3GS, it just has more pixels.
I think if you are interested in hacking the phone and changing the software, adding or removing UI, etc. the Nexus One is going to be the best. Samsung hasn't built community confidence in their OS upgrades, and the phone will certainly be more locked down for rooting and unlocking the bootloader than the N1. This doesn't mean it won't happen (it sure has happened for the EVO in a hurry), and I'm sure it won't by like my Backflip sitting here with absolutely no hackability, but there is a chance that it will be a device that you have to mainly use stock.
If you don't care about that, or if you want the best gaming hardware, the Samsung will probably turn out to be the better phone.