Ranger (Potential Multiclass) for a level 20 oneshot

So I'm gonna join a level-20 oneshot. I know the DM well, and he seriously enjoys combat, especially optimization, and I'll likely need to match that.

98% of my characters are rangers, and I'm debating whether to multiclass, and to what. Also, for ranger subclass I was thinking a Horizon Walker or Gloomstalker. So what multiclass would be most effective?

Also, I'd prefer my character be range-based, and I'll likely play an avian race.

Thanks!