There really are all kinds of "better". CPUs can be rated by pure performance, performance/watt, heat, performance/price. The AM2s and Conroes are just the latest technology.
When evaluating performance you could gauge by the relative operations per clock cycle * speed, but there are folks out there who have put together detailed comparisons between processors saving you from pulling out the calculator.
For server apps and mobile use, performance/watt, or how the relation of how powerful the processor is to how much power it will draw, and heat production are often more important than raw performance.
The Conroe is a huge chip for intel that finally brings them out of the very costly mistake that was netburst. The Conroe can outperform any AMD chip handily. The conroe completes about twice the action per clock as the P4 architecture it replaced and the smaller construction of the chips makes them produce less heat.
The AM2 platforms advantage over the 939 platform which it replaced is the use of higher bandwidth DDR2 and various instruction optimizations.
Things that will ultimately determine the performance of a processor are its clock speed combined with operations/clock, cache, and instruction extensions.