I think it really depends on the colors for the sona in question. Like mind changed between how he used to look and how he does now.
Originally it was a plain brown all over, and he had dark webbing on lighter brown fingers and body.
But now my current color scheme for my sona has a patterned and gradient of blues between his dark brown. So technically mine uses a lighter webbing. Though again it's really unique, so it's kind of a different situation. :\
Anyway! I kind of agree off the bat (no pun intended) that the darker webbing is preferable to me, but also again, it'll depend on your choice of colors. That will make a big difference!