>>57895011 (OP)>Arcanine vs. NinetalesArcanine has better stats but its' moves are awful, pretty much the only thing it has over Ninetales is access to Bite. Growlithe gains flamethrower at 49, but Vulpix gets it at 29.
>Slowbro & Starmie vs GolduckThis isn't even a competition - Slowbro is better in every way. If you need specifically a fast water, there's better options than Golduck, like Leaf Green's Starmie.
>Electabuzz & ScytherScyther might be cool, but it still doesn't do anything particularly notable unless it evolves into Scizor, which you can only get the metal coat for on the postgame sevii islands.
Electabuzz is a solid Electric type with great stats and some nice TM coverage, but its' role can be supplanted by Raichu or Magneton.
Of the Pokemon you're interested in, I think Leaf Green has the better exclusives. Fire Red's Oddish completely mogs Leaf Green's Bellsprout, though.