a 58.2% chance of success.
Running plays have a 67.9% chance of success (this number is higher than it should be because qb sneaks are included here)

QB sneaks have an 82.8% chance of success.
Non qb running plays have a 63.4% chance of success
all non qb sneak plays have a 62% chance of success.

It is stupid to ever call a non qb sneak play on a 4th or 3rd and 1 or less. If its 3rd and 1 you should do a QB sneak 100% of the time. If you dont get it at least its still only 4th and 1 or less and you should do a qb sneak 100% of the time again. If you dont get a yard after back to back qb sneaks then its just not your day.

Sample size of 3,181 4th and 1 plays from the 1998-99 nfl season to the 2015-16 season was used.

But im quite confident that any sample size of any time range in any years in any league would produce similar results.

QB sneaks also get more total yards per play than any other play ran on 4th and 1 and its not very close.
QB sneak = 1.61 yards
Non QB running plays = .83 yards
Passing plays = .84 yards