Might have to give this one to the Predator. His Plasma Caster would (in all likelihood) be able to do some damage to a T-800 type terminator. His other weapons? Probably not so much, as a T-800 type Terminator was shown as being able to still function despite heavy damage
However, the Predator, being mainly a hunter, might not want to go after a cyborg.
One thing though, a T-800 type terminator’s sensors would likely be able to track a Predator, despite his cloaking technology.
So it would mainly depend on who gets the drop on who first.
Also, the T-800 terminator should have other weapons available, besides just the M-134 Minigun.
I would give him/it the M-79 ‘Blooper’ (or ‘Thumper’) grenade launcher, lever-action 12-Gauge (or 10-Gauge) shotgun, and a Colt M-1911A1 (or Browning Hi-Power, not sure which Arnold used in the movie) pistol;