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If looking for quanity for 5. Hands down colorado!
If you use a guide your probability of success goes up greatly. If you have the money go with a guide. Also if your going guided I'd go to Montana with an outfitter that operates on private land. I can recommend a few if u decide to go that route
Whats your budget?
My first suggestion would be Montana Hunt and Fish. I used to guide for them and they have awesome leases. Although quite pricey.
Just a thought, the Canadian dollar is worth $.75 on a US dollar. I wonder if it would be worth it to hunt Canada? I may have to look into a buck buck hunt in Canada.
I would look to CO based on what you have listed so far since tags are relatively easy to get. Take a look at the success rates for various GMUs. CO has leftover tags that go on sale in early Aug that are 1st come 1st serve and they have good OTC access. CO has the largest elk heard in the country and does produce some quality bulls. One thing you may consider since you state that you are probably looking to make this an annual trip is to not get hung up on bulls for the entire group. You can purchase cow tags for about 1/2 the cost of a bull. So if 2 guys in the group get bull tags and the rest go for cows you are probably bringing home meat. I have hunted GMUs 421, 22, 511, 82, 86 and 12. Never had a problem finding animals if you are willing to hunt. Guide may be a good way to go for a season or two until you get to know an area. ATVs can be used in most areas just cannot use them off trails and other areas like wilderness. Hope this helps some.