Basics. The speed of the CPU is measured in Gigahertz. The higher the Ghrz the faster the Processor runs. Look for at least 1000 mb cache.
Go to Newegg.com or geeks .com they are usually cheaper there.
It's like buying a car. Everyone has a preference about the make but in general they are all the same. I personally like Intel but that's just my preference. What's important is speed both in the CPU and Video ram.
Hope this helps.