Hands down my most accurate handguns are my Contender(s) and my XP-100.
On a good day I can get groups about smaller than those of my best revolvers, and about half the size of tilt barrel autopistols, using the same ammunition. (Contender, with several different barrels)
The XP-100 (.221 Fireball) is simply rifle class accurate, being, essentially a bolt action single shot rifle with a 10" barrel and pistol grip.
I have revolvers and some autoloaders that can come close, but cannot quite match the accuracy of these single shots, despite being more accurate than the general run of revolvers and autos...