Sometimes the Liston people talk about online is not the Liston that really fought but some mythological creature - similar to Tyson or Dempsey. He was a great fighter but IMO lacks a bit depth in his resume to be truly called great (I don't think Schmeling was an atg either though). In the end it is Liston's physical advantages (size [they are the same height though], reach, strength, maybe power) and one of the division's greatest jabs vs. Schmeling's ring smarts, preparation, superior and more versatile defence, technique, speed and great right hand. The deciding factor IMO is if Schmeling can deal with Liston's reach advantage and jab on the one and if Liston can keep Schmeling on the end of his jab on the other side. That he can deal with great jabs Schmeling showed against Louis. The only one who had a bigger reach that he fought that I can remember from the top of my head is Max Baer who gave him a beating. However, Baer does not really use his reach advantage, so I'm not sure this can be seen as a good example. I think in 10 fights Liston's reach+jab wins him this more often than not, say 6-7 times. However, there is a decent chance Schmeling is using his superior hand and footspeed combined with his right hand to counter Liston silly like he did Louis (who was faster than Schmeling). Bottomline, Liston should be the fav but if I'd bet I put some money on Schmeling.
I wasn't really disagreeing with you, it's just I've always thought Sonny apart from his power, strength and great jab was also appreciated for his fine all round game. He was effective on the outside and equally as good on the inside, his upper body and head movement was good, I don't think there's that big a gap in technique.