Inspired by a previous thread, I did the math to determine what the best and the worst offensive and defensive Type combinations are, purely from a numerical point of view. Hopefully I did everything correctly, but do call me a faggot if I fucked something up.

As far as defense is concerned, the question is very straightforward, and here are the results

Best defensive dual type : Steel/Fairy
>Resists Normal, Flying, Rock, Grass, Psychic, Ice, Dark, and Fairy – 8 Resistances
>Doubly resists Bug – 1 4x Resistance
>Immune to Poison and Dragon – 2 Immunities + Status immunity to being poisoned
>Weak to Ground and Fire – 2 Weaknesses
>Neutral to Fighting, Ghost, Steel, Water, and Electric – 5 Neutralities

Worst defensive dual types : Ice/Rock
>Resists Normal, Flying, Poison, and Ice – 4 Resistances
>Weak to Ground, Rock, Water and Grass – 4 Weaknesses
>Doubly weak to Fighting and Steel – 2 4x Weaknesses
>Neutral to Bug, Ghost, Fire, Electric, Psychic, Dragon, Dark and Fairy – 8 Neutralities

and

Ice/Grass
>Resists Ground, Water, Grass and Electric – 4 Resistances
>Weak to Fighting, Flying, Poison, Rock, Bug and Steal – 6 Weaknesses
>Doubly weak to Fire – 1 4x Weakness
>Neutral to Normal, Ghost, Psychic, Ice, Dragon, Dark and Fairy – 7 Neutralities

Ice/Grass has one less 4x weakness but two more regular weaknesses, so in the end the grading system gives them worst place ex-æquo.
Offense is a whole other story, because we need to determine what best even means in this context. After all, dual-typed Pokémon don't attack with a Flying Press-like attack that has both their types into one.
After some research, I also found out that types combos able to hit every monotype in the game for at least neutral are somewhat common, with Ice/Electric (the famous BoltBeam) but also many others such as Normal/Ghost, Dragon/Fire, Dragon/Water, Dragon/Electric, Dragon/Ground, Dragon/Ghost and a few more including the winners.

Continued in next post