Deathclaws
Deathclaws I used primarily a Anti-Material Rifle because that is in my opinion and observation the only gun I've observed that allows you to kill a Deathclaw in one hit under stealth. Let alone, a few hits can kill a Deathclaw thats coming at you, as long as you fire it enough before it gets within arms length.
I agree and that's the first time I actually started using the Anti-Material Rifle. It really packs enough punch to take out the Deathclaws, which I hate with a passion! I could handle the Tunnelers and the Marked Man much better than those beasts. Thank goodness the Deathclaws are not there in an overwhelming fashion. You will deal with a pack of Deathclaws if you go check out "ground zero" (and a pack of Maked Men will jump you).
I also like to take up a high position and try to snipe Deathclaws. Most of the time, they don't know what hit them.
Now the Tunnelers will knock you over if they come within Melee range, I found that out the hard way. lol Close up, I used something that packed a punch, my .44 with hand loaded ammo, that'll shut them up quick. You will also pick up some Flashbang grenades at the beginning, those can disorient them for a bit. If they are in a pack and rush you, try to use those and then follow up with rifle.
For the marked men, I found that the Tribeam laser rifle does a great job! I'm not big on energy weapons, prefer my All American Rifle to those, but I found that I can kill the Marked Men far more easily with that Laser rifle.
So, I mainly used my All American Rifle, Tribeam Laser Rifle and the Anti-Material Rifle. I did have my .44, a sniper rifle and my riot shot gun as back up. Yes, yes, I always carry way too many guns with me... -.-
I just finished walking through the Divide and I must say, even with Tunnelers and Marked Men and Deathclaws... Lonesome Road is an amazing add on.