Bills v Miami. A few interesting ways it could line up. The most dramatic would be, winner wins the division, loser is out of the playoffs.
This is absolutely the right answer. First of all, I know that the past two years have featured teams playing for a wildcard spot, but it's still less likely, because it requires all of the other games that might be affected by that match-up to play out in a certain way. We saw last year that Seattle's win eliminated Detroit and meant their game against GB was no longer win-and-in (though it still ended up being exciting).
But also, the scenario where Buffalo-Miami is for the division is very plausible. RIght now Miami is 9-4 and Buffalo is 10-6. During the next three weeks, Miami has NYJ/Dallas/Balt while Buffalo has Dallas/LAC/NE. If Miami goes 1-2 and Buffalo goes 2-1 (both seem to be the most likely scenario) then Miami is 10-6 and Buffalo is 9-7. Since Buffalo already beat them once, they would win the tiebreaker if both teams finished 10-7, so Week 18 would be for the division.
Update: At this point, the only way Miami-Buffalo is not for the division is if the BIlls are unable to pick up a game in the next two weeks (when they play LAC-NE while Miami plays Dallas-Balt)
Only question is whether the NFL would choose another game if both Dolphins-Bills have already clinched playoff spots. I tend to think they wouldn't. For one thing, they've flexed games like that in the past (remember that great SF-Seattle game in 2019 where the Seahawks were literally inches away from winning the division?) For another, it's hard to think of many other potential matchups that would get the same ratings. Lions facing Nick Mullens and the Vikings? Minshew vs. Stroud? Browning vs Flacco for a wildcard spot?
Predicting the final game of the season is one of my favorite pastimes
Right now I'm leaning pretty heavily toward Buffalo at Miami. I just came up with one scenario on the ESPN Playoff Machine where both teams enter the game 10-6 and if Miami wins they're the #3 seed (over 10-6 Jacksonville) and Buffalo is out, or Buffalo is the #4 seed with a win and Miami goes to #7. That would be a great game to watch.
If the Saints can beat the Bucs in Week 17, and Atlanta can somehow win its next 2 (vs Indy, at Chicago) with Heinecke at QB, then Falcons at Saints in Week 18 would be for the NFC South with the loser going home. I don't see the Falcons winning their next 2 though. While Houston at Indy could have playoff implications, that's a game where someone might be eliminated before kickoff depending on what teams like Cleveland and Denver would do earlier in the day.
Otherwise, the pickings are pretty slim. These 9 games are definitely out because at least 1 team won't be hunting for the playoffs:
SEA-AZ
TB-CAR
Chi-GB
KC-LAC
DEN-LV
NYJ-NE
PHI-NYG
DAL-WAS
Jax-TENN
These games will probably be eliminated in the next couple of weeks
PIT-BAL (Steelers fall out of playoff picture)
MIN-DET (Lions are going to be locked into the #3 seed imminently and will be resting guys with nothing to play for in Week 18)
Rams-SF (if the 49ers win their next 2, they'll have the #1 seed locked up before Week 18)
Remaining games in order of least to most likely:
ATL-NO (this will be off the table if ATL loses in the next 2 weeks or NO loses next week to TB)
CLE-CIN (even if Bengals beat KC in Week 17, which I doubt, they will need a lot of things to go in their favor and will probably be eliminated by Sunday Night in Week 18)
HOU-INDY (will depend on the next few weeks, this game's importance will also likely depend on other results in Week 18)
BUF-MIA: The more I look at this, the more likely it seems. Rumors in Baltimore are that they might flex the New Year's Eve Ravens-Dolphins game into Sunday Night Football, which might mean Dolphins on SNF for the final two weeks of the season.