Why exactly are you upgrading? I certainly hope it's not for AH... An athlon 1.4 is quite sufficient for AH.
When you go beyond your current system, you may need to specify what programs you run that are causing you to upgrade. Then check hardware sites and look at their benchmarks, because at speeds above a generic athlon 1.4, you're going to see application-specific reasons to go for either Intel or AMD.
I have an Athlon 1.4 and wouldn't dream of spending a cent to upgrade it now, because I mostly game with AH and it's far more powerful than AH requires. As I type this, AH H2H host is running minimized, outlook express is running, I have slashdot in another web browser window, I run motherboard monitor, and the distributed.net client is also running. And nobody in my arena complains about warping and I can even fly with all that crap running with framerates between 50 and 100 (although I usually don't unless testing things.)
Again, if an athlon 1.4 isn't sufficient, then the application you use probably runs measurably better on either an Intel or AMD cpu, and you should find out FIRST before buying anything. Check for benchmarks that use that application or type of application before you buy, or you might get disappointed.