HI
I prefer to use AMDs And this has a lot to do with the instruction set and so on. Basically you can use a standard X86 assembler with it, whereas Intel (who actually came out with x86 chips in the beginning), have tended to move away from this standard with numerous chips that are appearing now.
I write bio-informatics software and use a lot of assembler code for speed. Add this to a 64 bit chip and I have a pretty good system with the ability to adress a hell of a lot more memory. which to me is important.
The AMD Athlon (64 bit version) has some pretty neat additional opcodes and so on too.
I used to prefer Intels (Pentium 1 and 2) over the AMD k5 and K6 but since AMD introduced the Duron and Athlon chips. I have pretty much switched over. Especially now they are bringing out 64 bit chips.
But if you just want to do emailing and word processing, getting a system with a 64 bit chip to do it is rather like using a warehouse as a garden shed.
If you want to do ultra realistic games or anything that involves a lot of graphical rendering, number cruching or something like that. Then it is useful.
All the best
Sophie.