Simple answer,, the one that's sharp at the time.
IMO, skinning in a shed is allot like cutting meat so any of the cheap (err inexpensive) knives the trapping supply houses sell will get the job done but I keep going back to that old Buck and the little Russel Woodswalker pictured above.
Skinning in the field's another story but I don't do much of that any more.
I added a KOA Cub recently that I have high hopes for .
There's a thread floating around here somewhere about it.
Sorry about the crappy pic of that GR.
Those scales were indeed beautifull