I've never bought a vibe before, which one should I get?

If you're buying your first vibe it should be multi-speed and not too big unless you're sure you like big. Something not too expensive is probably a good idea. Vibes that can be used either externally or internally (the cylindrical vibes) are good because they're multi-purpose. Other than that, choose soemthing that looks fun to you since this is the point—to have fun!