I agree that any "best ever" question is impossble to answer unless someone is omniscient of course, but then you knew I was going to say that didn't you?
I change my vote to Antares too...it's a technical tour de force, but it's very usable too. It's the skin that has pushed what's possible the furthest to date, AFAIK and IMHO.
As for the question about the first WB skin, Frogboy would probably be best placed here to comment but I think a few by Frogboy were "bundled" or available for download when I first saw and tried WB back in '98 (I think it was).
....though, a lot of those very early ones were at least inspired by previous works on other systems (Kaleidescope on the Mac for one perhaps). At least 18 of the skins listed https://www.wincustomize.com/skins.asp?searchtext=&sort=date&order=Ascending&library=1 look very similar to other skins I recall on previous systems or resemble other OS's....So I don't think that argument for the 1st being called "best" actually holds