Silver is quite a good rival in my opinion too!
Both are good, but here's my opinion on both of them.
Blue - This is the first rival. The rival that started it ALL. He has quite a History during the R/B/G/Y Games, such as becoming Champion, and possibly losing his Raticate. He is a very overconfident guy and is a bit like Silver when it comes to treating Pokemon nicely, but he had MUCH more success than Silver. Blue was a Rival, Champion, and a Gym Leader. This all happened in only 3 years. His team is sort of good (He, in fact, uses many Pokémon, and the Pokemon he has are very good in my opinion), but in my opinion there are others who have much better Teams, or is just a lot better than him according to treating their Pokemon. But I have to say, Blue is one of my Favourites, as Silver is one of my favourites too, but he is still quite flawed.
Silver - This is overall the better Rival in my opinion. He has got much more of a Rival Personality and trains some good Pokémon, ranging from Sweepers to Confounders (But his lack for owning many Pokemon puts this in a slight downfall, as you would know what to expect). He can still be battled when you're in Kanto, which actually makes this Rival much better, as Blue will only be found in Kanto. When it comes to building friendships, Silver is not the guy you would usually expect to be good at it, but as you come closer and closer to finishing the Game, Silver is kind of a bit kinder to his Pokemon. He isn't perfect, of course, nothing is perfect. Silver feels the need to call you "Weak" despite him losing to you every battle.
So yeah, the answer from me is going to have to be Silver. He has so many qualities Blue doesn't have. But please remember that Blue has way more Pokémon (Some of which are MUCH better than Silver's)...