I say go for Scizor.
Scizor @Choice Band
EVs: 252 Atk / 252 HP / 4 Spe (if you want EVs at all that is)
This Pokemon has stayed overused for the whole time it has been created. Also your team has some weaknesses that it covers (or tries to cover), so you might want that in local battles.
Your team is very weak to Ice types, Fire types and has very few counters for Dragon types, so I guess this one works.
In-game it can also use cut instead of U-turn / Bug Bite, which might prove useful later on.
Houndoom also does well though:
Houndoom @Life Orb
Ability: Flash Fire
EVs: 252 Sp.Atk / 252 Spe / 4 Atk
Let's see the in-game part though:
(Johto) Flying, Bug, Normal, Ghost, Steel, Fighting, Ice, Dragon
(Kanto) Rock, Water, Electric, Grass, Poison, Psychic, Fire, Mixed
Scizor covers 5 of these (with the given set) and 2 of Blue's Pokemon (3 during rematch)
Houndoom covers 7 of these (with the given set) and 2 of Blue's Pokemon (1 during rematch)
I'm telling you Whitney and Clair will be a menace (so will Blue and Sabrina), so I guess Scizor triumphs here.
Elite Four: Psychic, Poison, Fighting, Dark, Dragon.
Scizor covers 3 of these
Houndoom covers 1 of these
Well, so your best bet in-game might be Scizor, and your other alternative could be Houndoom.
Hope I helped!