I own both and I can tell you, they all have problems, but the sculpt of Sideshow's Snowspeeder Luke, even the non-helmeted head has the best likeness to my eyes and the helmeted head is my favorite out of all of them. The only thing better on the HT heads is the hair sculpt and paint.
I'll give you that the belt is better on the HT Bespin Luke, the SSC Snowspeeder Luke belt is a little lower in quality especially those damn annoying magnets, but the boots on HT Bespin Luke are about even. Although it's nice to have real cloth boots, they don't hold their shape very well and can easily look bad if not properly futzed with. The Snowspeeder Luke boots always look good, have great poseability, and match the plastic molded gloves that even Hot Toys would give theirs if they made this version. That is something I prefer with my figures, if the gloves are plastic then I also want the boots to be plastic to match.