IMHO the Core Duo is the way to go. The Pentium 4 was pretty much a mistake from the start, while the new Core Duo looks very nice. It comes from the same heritage as the Pentium M which has performed very well for me. AMD64 or Core Duo is my suggestion, with the AMD64 giving you a lot more performance for your money. If money is not a problem then Core Duo all the way.