Help Monotype

[PhantomUnderYourDesk]

Depends on how 'difficult' you want to your playthrough to be, what Types you personally like and where/how you'll get the Pokemon for the playthrough from?

Though if you want a Type that's not very common, how about going against all odds and use a Normal Type Team consisting of Kinetmunk/Eshouten or Spledifowl/Tanscure/Felinger/Kiricorn/Paraboom? They all have a secondary Type to bring some variety into things.
Dark Type feels interesting as well, and there are more Pokemon to choose from. Something like Tanscure/Belliadon/Tubareel/Chainite/Vilucard/Baariette?