In an interview on Sunday Brunch while discussing the release of Fun On Earth, Roger Taylor says he has Jeff Beck guesting with him. Then calls him 'my favourite guitar player, you know'. Quite a blow to poor Brian... link (4.55 to 4.59)
I don't think Roger was being disloyal to Brian, It's just that Brian is more like family to him. I mean if he was asked who is your favorite drummer, he would probably say "John Bonham" That doesn't mean he's being disloyal to "Rufus"
It's sort of like when somebody might ask "say" me, who is my best friend, I would say my mate who I've been friends with since childhood, when in real life, my wife is actually my best friend.