Andy,
A friend and I have been hunting Colorado for ten years or so. I'm sure our experiences relate to our area and how we hunt. We pack in with horses, then hunt very hard, getting into the secluded, nasty areas where the elk fire up. The hunt is a different experience every year depending mostly on the weather and hunting pressure.
The most exciting hunts are the late hunt. We like the last ten days. This usually coincides with the peak of the rut. Hunting can be tremendously exciting. Calling in several bulls in the morning, and one or two in the evening is typical. If the area has been pressured hard it's more difficult to find the elk....we still find 'em. They still fire up. Colorado has a lot of elk, and the rut is competitive and intense.
The bulls can be a little warrier later. However, if the weather cools, they fire up and lose thier heads.
We've had great luck on the earlier hunts too. A lot depends on the weather. If it's hot, you can hardly get a response, and they don't make much noise. If you get a cool snap, the elk will fire up, and come in easily.
The big bulls are always tough to hunt. Later on, they're herded up and don't leave thier cows. They can be goaded into a fight, but getting through all the satellite bulls to do it is tough. They might be easier to hunt earlier, but the hunting is slower.
All things considered, I like the late hunt better because it is often tremendously exciting.