i switched very early from sprinter/skeinforge to marlin/slic3r and went from laying pools of spaghetti to useful prints with virtually no other change. i attribute most of that to slic3r's less insane configuration settings.
the most noticeable difference when comparing the quality of equal parts between sprinter and marlin seems to be on the curves. sprinter will pause a bunch going around, say, a circle. it's not one smooth motion. it's more like it making a bunch of small straight lines in the shape of a circle. marlin can recognize the curves and do them in one big smooth motion, which makes for far better looking prints without all the "globs" from the hot end momentarily stopping over and over.
