Have stayed at 3 hotels in Gardiner as well as 3 inside Yellowstone National Park. All of the hotels are rustic in nature.
Understanding this, the accommodations at several places are nice. Personally, I prefer staying in Gardiner because you have several restaurant options, some with live music, grocery store access, optical equipment supply store (recommend a scope for best viewing opportunities such as wolves, grizzlies, eagle nests, carcass sites, etc), gas station without markups compared to inside the park (tip: fill up and clean windshield each night when returning to Gardiner), and some gift shops. ~10 minutes to Mammoth, with animal viewing on the way.
Pros: walking distance to several restaurants (Outlaw Pizza and Corral are favorites of mine. Wonderland Cafe is nice as well, but be prepared for waits, and about 0.8 miles away compared to 2-5 min walks to the first two mentioned above), blackout curtains, in-room binoculars, great views of river and mountains, covered fire pit with lounging chair surround…did not confirm, but potentially an outdoor fire pit as well, great for social visiting with friends/other guests, S'more kits for roasting at the fire pits (complimentary), in-room house service daily, plus changing sheets every three days for longer stays, nice room accommodations, fridge and microwave, and nicer showers than the other two I stayed at in Gardiner.
Cons: mattress comfort is not the best, parking limited and can be tight.
Trying the cabin next.