Information has been taken from the Pokemon DB dual-type chart and I have used some extensive Excel magic to calculate my results. Note that this chart lists type double-ups twice (e.g. Fire/Normal and Normal/Fire) so they have been filtered out accordingly.
So the most offensively super-effective type across all possible type combinations is the Ground-type, with 55 super-effective matches! Here is the whole list for reference:
- *Ground (55)*
- Rock (48)
- Ice and Fire (44)
- Fighting (40)
- Flying, Fairy and Water (39)
- Steel (36)
- Ghost (30)
- Psychic and Dark (28)
- Grass and Bug (27)
- Electric (26)
- Poison (24)
- Dragon (16)
- Normal (0)
And across only the used type combinations, again Ground-type is the winner:
- *Ground (48)*
- Ice and Rock (41)
- Fighting (40)
- Fire (38)
- Water and Fairy (34)
- Flying (33)
- Steel (30)
- Ghost (29)
- Electric, Bug and Dark (26)
- Grass and Psychic (23)
- Poison (21)
- Dragon (15)
- Normal (0)
This was fun to calculate!
Hope I helped. :)