I'm surprised barely anyone has said water type. I believe it's a type with almost the most pokemon out there, and with only two weaknesses, there are plenty of pokes to balance things out. Also, there are offensive and defensive ones.
For example: Swampert, Ludicolo (oh look both get rid of weaknesses), Poliwrath/Gyarados for offense, Starmie as a spinner, bulky waters like Vaporeon for stalling or healing.. you get the idea.
end_boss said:
But fast forward a bit and I think that my definitive Type choice would be Fighting.
I don't care too much for Fighting as a pure Type, but most of my favourite characters have a mix type with Fighting. Heracross, Infernape, Lucario, Toxicroak, Poliwrath, etc. Besides, I realized shortly after that being a Fighting focused team puts me at an advantage over his Steels.
If I were playing just for fun more than strategy, I would do this too. I would right away want to throw in Infernape, BRELOOM!, Poliwrath.. there's three from very different types. I like all the dual types that fighting has.