Welcome. If you're done travelling for '05, I recommend Delta. My impression is it is easier to redeem miles with DL than with NW. If you have more travel in '05, you will likely earn low/mid-level elite, and if so I recommend NW. This is based on NW's better mileage bonus for Silver elites (50% vs. 25%), and my belief that silvers and golds have better chance to upgrade to FC on NW than on DL...Pity you can't book on American.
Transferring miles is not free with either carrier. Maybe others know of some workarounds; I don't.