I’ve hunted both multiple years. I’d say Colorado. I think the theory on Colorado is that it’s jam packed with people and you can’t get to the spots you want to get to. What I can tell you is that in some units that is absolutely true and I’ve hunted in and around a lot of pressure in CO. But on the same note, I’ve had some of the best hunting experiences of my life in Colorado. Just outwork other people, stick to whatever plan you have, and know that there is a ton of space out there and a ton of elk.
On Montana, I do love hunting MT as well but I honestly have run into more people in Montana than I have Colorado. The other part of MT is that you virtually have to be ready to hunt in G bear country no matter where you go out there now. For some, being mentally prepared for that can make or break your hunt. There are great elk hunting opportunities in MT and you may have a chance at a bigger bull, but I’d still go Colorado over MT.