Bruce Arians .
Living here in the Indianapolis area, I've been very impressed with the job he's done in the roles of both HC and OC since Chuck Pagano's illness. He definitely has his team "playing to win", rather than "playing not to lose". Yesterday's close game with the Titans is a good example. Less than 2 minutes to play, Titans out of time-outs, Colts ball on their own 25 yard line, up by 4, 2nd and 8, and he has his rookie qb throw a 12-yard strike to his rookie TE over the middle ...(which looked to be into tight coverage!) Luck got the completion, and the Colts did the "victory formation" to win the game.
MOST coaches probably would have played it safe at that point - run as much time off the clock as possible, punt it, and hope the defense could prevent a last-second touchdown. But Arians showed confidence in his offense, and it paid off. They've won 8 out of 10 since Arians took over for Pagano, and almost every win has been close, "gutty" football, requiring key calls in key situations, good clock management at "crunch time", and a willingness to take some risks - everything the Bills currently lack.
Colts expect Pagano to be back on the sideline by the last game of the season, (and hopefully into the playoffs). I don't know that Arians would consider taking a HC job somewhere else next year if it were offered - but he's at least the TYPE of coach I'd hope the Bills would go after if they get the chance.
GO BILLS!