I remember years ago somebody on this forum said "Alaska is Class C Country" and it's true. We've made many AK trips to visit family and friends. Some of what we learned:
Great Alaskan seems to be the "boutique" of the rental agencies. Beautiful facility, their own factory certified Ford and ONAN service agencies, and Winnebago-built rental (Chalet series) coaches. They also sell Itasca and Winnebago A's new. The majority of privately owned C's in Anchorage seem to be former Great Alaskan Chalets. They sell them "young" and so well detailed they appear new (in their boutique indoor showroom!).
ABC is more of a dirt lot operation. We rented from them, and they were completely cordial, helpful, and responsive when we had a failure (furnace logic board) down on Homer Spit. They were renting Gulfstream units. We later learned how helpful they can be to both buyers and renters from other companies. ABC is one stand-up outfit.
I wouldn't hesitate to do business with either, nor to buy a Great Alaskan former rental. You may like how they "train" the renters. Great Alaskan sets them down in a designer cubby to watch a video. ABC makes sure the coach isn't "parked in" by others and hands over the keys. Both, of course, offer a walk-through. Both companies offer trip planning based mostly on how much time you have.
Fraserway is a Canadian outfit. No experience with them, but I believe they're the one that rents lots of truck campers on diesel pickups. Lots of them out there too, but nothing like C's.
On the westbound side of AK HWY entering Watson Lake sits "RV Services" (and they offer a slight fuel discount for RVs). Steady stream of rental C's there too, and the staff commented most of the renters are European.