The laptop processor is typically lower-powered processor than those which are found in desktop machines. Processors that are designed for mobile computing consume less power. They are very cooler than desktop processors. Then only your battery will last long. The desktop processors have fans to cool them down, but it is very hard to fit that tiny stuff into laptop because laptop batteries will be drained by the fans. Those who use laptop must know the term TDP which means Thermal Design Power. Those who want cooler processor can go and buy the lowest TDP.
The performance of the laptop depends upon the characteristics that differentiate laptop CPUs. They contain safe memory, speed etc; the mainstream processors contain double cores. Cache memory helps for the speed which allows CPU to keep from accessing slower main memory, but the speed memory determines how fast the processor talks to the rest of the computer. They have different capacities.
If we want to get the full details about its performance we have to look at specialized comparisons or benchmarks The best performance can be had with the use of Intel which currently rules things with its core 2 Duo processors. We should go in for Intel core 2 Duo and should also go for the T7XXX series. If you are going in for AMD processors, no doubt they too will work fine, but you may not get the top-end performance. Never be conservative and go in for the cheapest it will always be lowering your data.