Uh, Vaporeon and Gyarados. Two great Pokemon. :D
Well, let's do stats first. They both have two base stats over 100, Vaporeon has high stats is HP and Sp. Attack, with another great Sp. Def stat. Gyarados has a high Attack and Sp. Def, as well as another great HP stat. Unfortunately, Gyarado's Mega Stone can only be found post-game, therefore we're still left with this dilemma.
Thinking attack-wise, Vaporeon has a high Sp. Atk - moves like Surf and Hydro Pump are great with STAB applied as well. But Gyarados and it's Attack doesn't allow as many good STAB physical moves, maybe only Aqua Tail and the sorta-worthless HM Waterfall. However, it can learn some non-STAB moves like Earthquake. Honestly, STAB is a great advantage so Vaporeon could be your best bet sweeping, but being a wall it would have no use, except for it's high HP. Gyarados, no better, has a great Sp. Defense stat and rather decent Defense stat, hence it could be your best bet as a wall.
So, if you wanna special sweeper, go with Vaporeon. If you wanna special wall, go with Gyarados. Vaporeon does have the extra high HP to go with the average defensive stats as well as it's high attack stats, therefore I would go with Vaporeon. However, it is your choice. :3
Hope I helped. :)
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