depends on what you are trying to do. If you want to call and chase, go later, but remember there is a muzzleloader season in there, and many areas of Colorado public land are not so great for calling (bugling) any more.
Early is warmer and the elk are not as sexually active, but they are still there and available to hunt, not yet so well chased.
Bear season doesn't start till a week or so after the elk season so if you are getting multiple tags, count on that too.
Lots of choices.
ChuckC