I think it's fine to have 'friend' characters, but if they're not really a proper competition for you, they're not exactly a proper 'rival'.
However, this isn't me saying mean rivals are better. I mean, I think there's a lot more to it than just friendly/mean.
For an example, Barry is one of my favorite rivals, because you're always competing with him and can have a serious battle, but in the end, you'd have both had a good time, and when things get serious you know he has your back.
Cheren, Hugh and Calem/Serena kind of have the dynamic of an actual competition, but they feel too serious and depressed when they lose. Hau seems close, but a little bit too far in the other direction in that he doesn't seem to care about winning enough.
The likes of may/bianca are fine as "friend" characters, but aren't really rivals in my book. Wally could've been, but didn't show up enough.
As for Blue/Silver; they're more just like an enemy. like, you're never really happy to see them, they're not someone your competing with (Blue maybe I guess) they're just in your way. Silver is a good character because of his development, but not necessarily a great rival.