Blenheims are my personal favorite, but of course, I think they are all beautiful. I went to a National Cavalier Specialty show last December, and I attended a conformation seminar there. I noticed that whenever the judge/teacher would show a video of a ruby, lots of breeders in the room would ooh and ahh a lot. And I think I remember them talking about how rubies are discriminated against in the show ring compared to the parti colors. They seemed to be cheering for the underdogs, so to speak.
A breeder I had been talking to about buying a puppy told me about a show she was entering some dogs in near me, so I went to see her and them. She had a b&t very young dog who didn't place, and she commented on how hard it is for b&ts to get noticed/placed in the show ring. She definitely felt they were discriminated against.
I think the parti colors are just much more flashy and showy compared to the whole colors, so they grab the judge's attention. Of course, a good judge would be impartial to color, but maybe some aren't.
On the other hand, I did a little bit of work with Lucky Star, and the two dogs I rescued were b&ts, and the lady at Lucky Star said that was a positive in terms of being adopted because she said everyone wants black and tans, and they don't get that many into rescue.