One of our very favorite places - Glacier! A few trips there for us and never tire of it.
Depends on what you are looking for IMHO.
We prefer the East Side as we like to hike, walk, etc. The West Side is the commercial side.
We definitely prefer and recommend the KOA on the east side and have looked at the alternative but never stayed there. And, if you choose, you can cross over into Canada and go to Waterton Lakes (not sure of passport requirements now). Much more laid back area.
The KOA on the West Side is the best place on the West Side - and we have looked at several. But we stayed there only once due to high cost and plenty of amenities we don't need. We have mostly stayed at North American.
We like to hike and I do my photography work. So much depends upon your interests.
Feel free to PM or email me if you would like.
Enjoy - fantastic place!