AMD Absolutely for certain.

AMD chips have a lower frequency rating than Intel chips but execute many more instructions per cycle. What matters is the number of MIPS (millions of instructions per second) that can be executed. When Ihave used Intel chips the MIPS rating is about the same as the frequency, not true for AMD :

Some chips I have used :

Frequency MIPS

Intel 500 500
1000 1000
AMD 500 1000
1000 3010

Also AMD chips use less power so they generate less heat. Basically this means you don't need such a big fan. The fan for an AMD chip is about the size of a cigarette packet, for Intel about the size of a half brick!

AMD have achieved better designs and power consumption by better using CMOS technology obtained in a technology transfer from the Russians.

Also AMD produce both 32 and 64 bit chips which are useful for high throughput applications (but only Linux takes advantage of this).

Also you might want to Google "Wintel duopoly".

Used to go for AMD, but the intel quad cores work so much better than their amd counterparts

Its a real shame that AMD is struggling. A few years back they were really scaring Intel. As previously mentioned achieving the same performance but running at half the clock speed is like putting a car in top gear - its more efficient and more clever. Unfortunately Intel has got some of their heat and power issues sorted and is pulling ahead. AMD's current chips are sloths. I wonder if Mac's (fairly) recent change to x86 has given Intel a little boost

I'd say AMD, more value for money.

I have always used AMD

at the moment their is absolutely no reason to use an amd cpu, even their phenom cores are sub standard. i build pc's for friends and family and i will pit my own personal pc against any amd powered one. i have a quad core intel at 3 ghz, 4 gig of ram, a 500gig sataii harddrive, and a p45 motherboard, all running with a 1600 fsb