Probably Colorado. Donāt let anybody talk you out of it. Pick an area that has high numbers and not known for trophy bulls. Idaho MT and WY are likely better quality. Success rates are low, not because elk hunting is an impossible task. Itās because 95% of elk hunters donāt care, are lazy excuse making pussies that will go out of there way to quit after a day or two of being discouraged.
Greenhorn pretty much nails it, you are late to the party in ID and WY at this point so just pick a CO unit and go, it's not that hard, relentless forward progress for two weeks and I bet you get a bull, most people just throw in the towel after two half ass days...
As far as advice goes:
1. Get fitter, the western mountains surprise most first-timers even if they think they are fit, you really can't have too much in the tank, covering ground finds elk and if you can't do that then you will be one of the 90% that never punch a tag.
2. Don't marry a spot, if there are tracks at a spot that don't have an elk currently standing in them they are not a reason to sit there for a week, be mobile, camp at the truck and go into different drainages every morning and evening until you find the activity you are looking for, elk are rutting somewhere if it's not where you are then you need to keep moving until you find it.
3. I'd pick a unit based on terrain, not so much for success rate, stats are easily skewed by private land and many other factors, buyer beware... better to decide what type of terrain and style of hunting you prefer and make your location choice to have as much of that type of hunting as possible, for example, I hate hunting flat dark timber, I'll take a unit that is mostly alpine terrain or oakbrush over a flat dark timber unit any day, even if the success rate in the timber unit is significantly higher, someone who loves stillhunting through timber would likely hate my preferred spots...