|What do you mean by better?|
The K6/2 was cheaper, but only went to 550MHz, while the PIII was pricier but went to 1.4GHz. Plus, the Pentium III supported 133 FSB.
This question is relative to the time frame, as time went on you could find a AMD that would perform better than a PIII.
iMac G5 1.8GHz "Hero" PowerPC
2 x 1GB DDR PC3200 SDRAM
160GB WDC WD1600JD-40GBB2
Mac OS X Leopard Version 10.5.8