Hi,
Sadly, the best answer I've been given seems a bit smart alecky, but here it is: "It's the ammo that shoots most accurately in YOUR gun."
Now, what kind of accuracy do you want/need? Bulk pack stuff's fine for killing cans, and in some guns shoots well enough for pest control. "Mid-grade" such as CCI Blazers and Mini-Mags have served me fine for "a little more accurate" such as one wants for rabbits and squirrels a little further out. I don't need target accuracy, but the Winchester T-22 was a favorite of the guys shooting the .22 events at our local silhouette matches.
But only testing will tell you what fits your needs. Sorry...
Rick C