Type? I'd probably say the new Fairy-type. So many of the new Fairy-type 'mons have fantastic Special Defense and Special Attack stats, which let them take lots of hits while dishing out damage. An immunity to Dragon-type moves is definitely nice as well.
As far as individual Pokemon go, though, I'd have to say the Squirtle line, simply because I speedrun Pokemon Blue and in those runs Squirtle (and it's evolutions) are the only Pokemon I use for the entirety of the run. Plus, Blastoise's new Mega-Evolution is pretty cool, and can run a mean Mega Launcher set with Dark Pulse / Water Pulse / Dragon Pulse.