I like the P4 S423 as the worst, perhaps with cacheless Celeron as a close 2nd. Cyrix 6X86 and AMD K5 were pretty crap as well, but I don't rate them as badly because their pricing wasn't horrible. 6x86 was actually okay for general Windows nonsense, just horrible at most gaming due to the almost complete lack of any FPU performance. K5 was pretty crap, luckily K6 fixed everything and was much better. Too bad Super 7 chipsets sucked for the most part, limiting the fun with the K6-2/K6-3. Best : Athlon XP Pentium 4 Northwood What a fantastic rivalry that was. On either you could get a cheap low-clocked one and OC to top-tier levels or beyond for bargain pricing. Core 2 Duo / Core 2 Quad might take the cake though. Still usable today for many things, much faster still than crap tablet processors, and a 3.4ghz+ C2Q will still run basically any game out there.