AM2 provides a better upgrade path. Not to mention I saw this freaking incredible mobo:
Mad options for OC, 802.11g, and the nForce 590 chipset make me want that now, and I might go when the prices drop on the new AM2 chips.
AM2 also has the 5000+ X2 chip, which is probably close to the FX in performance.
I would say go AM2 because of the better upgrade path. Future processors will likely be AM2.
Of course waiting till July 23 to see what Conroe can actually do would be a good path as well.