I'd choose a electric-water type due to it having only 1 weakness,but you can have an air ballon on him. Electric covers the weaknesses of water,(grass and electric)and the ground weakness is still there.
A Dragon-Steel type would also be good. Steel covers the Ice weakness, it also covers the dragon weakness. Fire is also weakened to regular power. It only has two weaknesses,ground and fighting types.
Finally, a psychic-dark type would do swell. Dark covers two weaknesses of psychic, dark and ghost. Psychic covers dark's fighting weakness so the only weakness is bug,ut bugs can be killed easily due to their common weak defence stat, even if one bug type move could kill you.