My CPU history...
1a. Intel 486 (bought)
1b. Cyrix 486DX2 (upgrade)
2a. Cyrix P133L+ (built)
2b. Intel MMX200 (upgrade)
3. AMD Thunderbird 1200 (built)
4. Intel P4 3.2GHz Prescott (bought)
On that cycle, my next system will be a self-build AMD - actually, that's what I was planning until this supermarket special came up, working out cheaper than comparable parts.
At the moment, I'd say AMD have it, on price, performance and power efficiency - the Prescott gets hot and bothered far too easily, a bit like a certain oaf of a politician!