IMO I'd get the phenom as 4 true cores tends to be better than two hyperthreaded cores. The results obsidian posted are very interesting tho, they show that they're quite equal. However that doesn't take into consideration overclocking, tho both can OC pretty well.
The other consideration would be the chipset/mobo. I think the AMD high end chipset has maybe a little bit better features than the P55 chipset and generally for a little less money. But quite often, the better features won't even be used.
Overall, either will be a good choice. They both have pretty decent upgrade options. You could get an X6 down the road on the AMD platform, or an i5 760 or even an i7 870 with the Intel system.
So basically, they're pretty similar. I think the best bet is to put together a list of components, and see which will cost less or allow for better components. Maybe with AMD you can squeeze in an SSD? Or upgrade to a higher tier video card if you game a bit? Hard to say to pick one over the other without doing that.