Theoretically, the most accurate small snub is probably the S&W Chief's Special with the rare target sights. They've never been catalogued but a number have been made over the years. Model 50, I think.
Go to a medium frame, and their M19 and M66 have been made in 2.5-inch barrel length. Ditto the M15.
The Colt Python in 2.5-inch length is larger, but superbly accurate. It does lose its cylinder timing sooner than the S&W mechanism, though.
Practically, if the fixed sights on a typical good "service" style snub are "on" for the load it likes best, you'll be astounded at how well some shoot...in the right hands!
Lone Star