I have some experience with the optics listed.
Sightron SIII, Leupold MK4, Burris XTR.
The Sightron has the best glass of the three, but not by much over the Leupold or Burris. I had my Sightron SIII 8-32x56 next to my Leupold MK4 4.5-14x50 for a while comparing the two at 14x. While I know that the exit pupil is slightly higher on the Sightron (4 vs. 3.57), the contrast and clarity were just a hair better with the Sightron. The glass on my Burris XTR 3-12x50 was just a hair behind my Leupold again in contrast and clarity, brightness at 12x was even. All in all there isn't much of a difference between the three, not enough that you would notice without putting them side by side.
The adjustments on the Sightron are the most tactile and audible of the three. The Burris is somewhat behind with decent feel to the knobs and some faint noise during adjustments. The Leupold MK4 as it came to me is far behind. The turrets feel as mushy as my Super Sniper. I'll probably take the caps off and play with the o-ring when I get tired of it, but for now I'm not going to mess with it as the rifle it's on is shooting great.
All three scopes have been absolutely repeatable to me so far.
Hope this helps a bit.