[Steve gives this some thought, still a tad vague, but he can work with it]

Are you looking for a particular type? Like fighting, water, electricity, flying, so on and so forth?

Besides that, some fast but strong Pokemon are Aerodactyl, Weavile, Tauros, and Infernape. If you want strong but fast, try Garchomp, Staraptor, and Scyther.

[Steve has done a lot of studying to figure out Pokemon he might want... that and a quick check of the Dex helped]