Oh my word... after much research on my part... We just pulled the trigger on a 2011 313RE. So I will spew as much as my reasearch as I can. Here are most of the items that was important to us when we looked. We wound up buying a 313RE High Country.
Montana
1.) 1/2 shackles and wet bolts are now standard
2.) Hardwood stiles around the cabinets, not just the doors
3.) Fiberglass back cap with backup lights ( same in my HC as well) no rear bumper, but most do have a hitch. (HC is looked at did not have hitches.
4.) Same ol chinese goodyears
5.) Name brand electronics inside Samsung...ect..
6.) Usually a little heavier
7.) A little thicker Gelcoat on the sidewalls (outside) ( same in my HC as well)
8.) More insulation R-21 floor R-34 roof R-9 sidwalls
9.) Slam baggage doors with hydraulic piston assist.
10.) Electric front jacks all the rear jacks I saw on the Montanas were electric ( same for HC)
Mountaineer
1.) 1/4inch shackels and plastic inserts ( same in my HC as well)
2.) Hardwood doors on the cabinets, wood grain sticker material on the stiles. ( same in my HC as well)
3.) Standard backcap with integrated backup lights, They usually had a bumper as well, Spare mounted to the bumper.
4.) Same ol chinese goodyears ( Towmasters on my HC
)
5.) Electronics are Visio no name brand types...( same in my HC as well )
6.) Usually a little lighter not by much ( HC is wayyyy lighter )
7.) I found that the gel coat outside walls is not quite as thick as the montana.. Could just be me tho. and the mountaineers I looked at.
8.) R-14 in floor and roof R-9 in sidewalls (Unfortunatly I dont know what the HC is.. if I had to guess Id say its the same.)
9.) Standard no slam baggage doors.
10.) Electric front jacks optional electric rear jacks ( some you would have to use a powerdrill or something).
The most important part is floorplan. You have to like what your living in. At least that was the most important to us. Im pretty mechanically inclined so Ill add the 1/2 shacles and wet bolts down the road. As well as a 5th airborne or Mor/ryde pinbox if needed.
I would also add a good TPMS system as well. Tyron comes to mind.
Hope this list helps.