I've hunted both pretty extensively since 2009. After my first hunt in 2008 here in NM, there's no way I wasn't hunting elk somewhere. With the CO border only 3-1/2 hours away,it was a no brainer for me.
A few differences of note from my perspective.
The terrain! The Sangres in Northern NM are as steep as anywhere I've hunted in CO. CO is steep in every unit I've hunted. Google Earth doesn't do it justice by any means.
Although nowhere near as steep or high in elevation in most units I've hunted in NM, the terrain here has its own challenges. The grass covered rock here can be brutal on your feet. The constant up and down because mountains are shorter and ridges typically don't run nearly as long as those long ridges in Colorado. Both states are extremely physical.
Water availability is a stark contrast. In CO it's nice to be able to filter water when needed. It's usually not an issue in CO. Elk obviously don't have to travel very far to water.
In NM water is at a premium in alot of units and you see the kind of distance elk will travel from feeding/watering to bedding areas. You're better off if you are able to figure those travel routes out sooner than later. As a hunter you have to have plenty of water at the truck. Sucking dirty cow piss filled stagnant water out of a dirt tank is still something I refuse to do. I'll take the weight penalty to stay alive.
In CO yes there are plenty of forest roads. But they are spread out. You can typically park and hunt, move park and hunt rinse and repeat hunting alot of areas that get overlooked. You can also hike a mile in, set camp up and hunt vast areas without having to hike into wilderness areas. And you can hike into wilderness areas, set camp up and hunt that way too.
NM has very few wilderness areas comparatively speaking so truck camp is more conducive here.
The obvious where OTC is concerned is the pressure, or lack of. NM doesn't have OTC obviously. However the draw units aren't much different pressure wise. Well that was true 5 years ago anyway. Some of the units that have become draw in recent years are a draw unit on its face. I hunted a draw unit on the Western Slope last year and there were more people hunting it than when I hunted it in 2016 when it was OTC. So some of these new draw units are overcrowded.
I've hunted other draw units in CO where I never saw another human unless it was on the road system.
The vegetation is night and day in the 2 states. 75 miles or less from the border in NM, you'll notice huge changes. Going from spruce beetle kill laden forests in CO, to healthy pinion forests and the dry high plains desert vegetation. Diets are totally different.
In NM I very rarely come across wild strawberry's. In CO I've found wild strawberry's and wild raspberries in abundance. One of the few things that take my mind off the task at hand. I literally drop to my knees and gorge like an Alaskan grizzly.
I've been in the Gila and it smelled like an onion. I will get my fill of wild onions as well. And they seem to have a hydrating value as well.
In CO the drainages can be so lush with some type of willow or alder growing in them bushwacking is impossible and they can be marshes where you'll find that out as soon as you sink up to your knee in muck. And the deadfall. Oh the deadfall.
NM you wont see a whole lot of that. There will be deadfall in most forests or where there have been wildfires, but typically it doesn't hold a candle compared to CO deadfall. You literally better be able and willing to carefully tightrope, or you're not going thru and will have to find another route in CO.
When it comes to the hunting differences whether an otc unit, or draw unit in either state, my tactics don't change much, however as I continue to learn and unlock the elk code, my tactics have evolved. I'm doing a few things noone ever talks about and have taken what I've learned from a few great elk hunters (some from right here) and what elk themselves have taught me and continue to try new things.
I won't be pigeon holed into hunting a certain way because it's the next best thing since Wonder Bread. Growing up, Bruce Lee was my hero. So staying fluid and adaptable has become a big part of how I hunt. I take pride in being able to change tactics on a dime. There are many who are 1 dimensional. My tactics are very versatile. The versatility has allowed me opportunities in a dozen different units. I am confident before ever stepping into a unit that I will find them.
One of my early mentors aka Da White Shoe (Zane) once told me "David, a confident hunter is a dangerous killer". And he's right!
another man i look up to (Lou) has given a ton of tips on the forums that I've personally taken to heart, and now I spend alot of time just listening and in doing so, I've heard sounds elk make that aren't raging screaming bugles, but subtle quiet sounds that many have probably heard and never paid any attention to. Hearing these different sounds has put elk in my freezer. And taught me alot of patience.
My good friend JPD350 on the forums has been so instrumental in helping me learn where elk are, what they do and when they do it. He has been instrumental teaching me how to find elk no matter where I'm hunting. There is noone better at dissecting a unit. Having mentors is invaluable.
So the differences in hunting elk no matter which state you hunt, should be fluid and adaptable. Once you have this, there isn't a whole lot of difference hunting them. But let me say this. The factors I listed above may alter my approach slightly, but tactics don't change because of it.
Lou once told me "if you pay attention to what the forest and the elk are telling you, you will learn how to hunt them. Elk are great teachers". He also told me "elk are incredibly good at the survival game. They play it all year long".
True for all states and countries world wide.