Its pretty much a preference thing. AMD X2 are quick but only marginally faster than intel, they are also alot cheaper. If you are building a new box, dual core is the way to go for sure.
I built a D system this summer and it was based on a Abit Aw8 (intell 955 chipset) with a pentium D 2.8 and it was a screamer. A dual 3.0 core may not be faster than a 3.4 (and only marginally, the difference is about what, 3%?) BUT it is a dually so you will be able to do more things at once (very good) and it will run multiple processer apps (VERY VERY GOOD) so in my mind, I would not even consider a 1 way chip these days. Once you go dual, you wont go back.
As far as AMD vs Intel, Where ever you heard that X2 is better for recording, they are wrong. How good a chip is for recording is the sum of the parts and how they work togheter. Yes AMD holds the speed record right now and the 5 towers (cubase benchmarking site) has Opterons holding all the top spots but those chips are about $300-400 more than any pentium 4.
I think my biggest gripe with AMD is the overall quality of the systems (and I administer a network for a living). We run a mixed environment of about 20 machines split 70/30 with the majority of the machines being AMD XP/Semprons on via chipsets. Of those machines, I have had various problems with about 1/3 of them where on the intel based machines, that number is 0.
I think the chipsets are just weak and poorly implemented.
For music, I want stability over bleeding edge performance and I have yet to see a decent, non-opteron AMD based systen that offers that. My intel box has been running non-stop since May (when I moved, I dont turn my machines off) and never crashes, freezes, or otherwise gives me problems