I've said it before and I'll say it again: Blue is the best rival for the sole fact that he is the only one who ever makes you want to improve and be better than you are.
All the other Rivals are like "lol dang you beat me! Next time I'll get you! (not)"
Sure, Blue is the same way, but his attitude STILL makes you want to improve (even though you know you'll probably beat him anyway) and like someone else already said he's always one step ahead of you plot wise.
Silver has some plot development ("Why can't I win-- Oh right I should like my pokemon *crobat*. Also, my daddy didn't love me!")
May/Brendan are awful just like their awful dad who is an awful Professor and gets punked out by a Poochyena
*THUD*Barry is a spaz. An annoying Spaz
Cheren has slight character development outside of being a typical jobbing rival (his character arc goes in the opposite direction of Blue; he's not bitter about others being better, and instead wants to further fledgling trainers instead of trying to establish dominance over other strong trainers (like Blue))
Bianca sucks for being the give up girl who because another May/Brendan (though she's a better trainer than them as someone already pointed out)
Hugh is pretty bland and like all of the other rivals not named Blue he doesn't really push you at all. Though ironically the whole time he is explicitly verbally pushing you to be stronger: "Hey best pal, you beat me (again), but I need you to get better and help me achieve my goals!"
And if N counts yeah he's best or second best up there with Blue. "Show me the power of your convictions!" is always badass
Wally is mid tier because you don't see him enough
Why don't we show them the entire process including our breakdown. http://i.imgur.com/Q0xhR.png?2?6330