Check next years CO season. It was scheduled to end early due to normal calender process, but that would have put muzzleloader in the last week instead of the third week so I believe it has been modified so we actually have late Sept ending next year.
I personally like the first week or the last week. The first week you can find elk lots of places not too far away from access. Not much bugling, hot, and busy are the drawbacks usually.
The last week is usually more vocal, cooler weather, and a little less busy. The drawback is 3 weeks of previous pressure including muzzleloader, and many bigger bulls have cows so eventhough they sound off, they aren't looking for company.
I like the last week, especially on public over the counter hunts because I can at least find elk due to bugling a bit easier. Another plus is the aspens turning.
Everything I just listed is just general, on a given year, the weather, temps, pressure, and bugling can always flow differently.