I'll give you a comparison:
Lets say you have 2 runners. One guy is tall, one is short. The tall guy would be like AMD, and the short guy like Intel. Let's pretend that how fast they can move their feet is like the frequency of a CPU. If they are both running at the same speed, the short guy would have to move his feet a lot faster to keep up with the tall guy. This means that the tall guy goes further with each stride.
AMD can perform more instructions in a single clock cycle than Intel. This is why AMD can keep up with Intel with lower speeds. Another thing that helps AMD keep up is their on-die memory controller, in place of Intel's Northbridge.
Which one is better? Well, I'll put it this way, do a search for AMD vs Intel, and see how many little locks are on those threads