I measured Speer and Hornady balls for comparison once and the Speers were more uniformly round. I believe that holds true even though that was just a one batch sample. But I don't think that alone is enough to make too much of a difference, and a riflescope might be needed to really tell.
My all time favorites are Buffalo Bullets round balls.
But they aren't easy to find and have become relatively more expensive online than the local offerings.