I don't put SW up there in this category, simply because his harmonies (which are always great) are often his voice overdubbed multiple times (although there are exceptions, like when Maitland was in PT, or when Wesley guested on a PT record, etc.). Same thing with Queen, whose harmonies were incredible, but layered beyond belief.
When I think of the best harmonies, I think of the bands who do them naturally, with no studio overdubs or anything. Bands like:
Yes
The Beatles
CSN(Y)
Eagles
Doobie Brothers
Styx
America