Which two type combos are most effective defensively and offensively?

Question

Basically, for the offensive one it should be resisted by nothing or close to nothing, and the defensive one should be immune to or resist the most possible types. Thanks so much!
Remember, only combos of two types, please!

Answer 1

I believe the two best types, STAB-wise, are Water and Dark, hitting 308 Pokémon supereffectively, 463 neutrally, and only 7 not very effectively. The best defensive typing is probably either Fire/Steel (weak to 3 types, neutral to 5 types, resistant to 9 types and immune to 1 type) or Steel/Ghost (weak to 4 types, neutral to 2 types, resistant to 9 types, and immune to 3 types).

In other words, the Pokémon with the best offensive typing are Mega Gyarados, Crawdaunt, Sharpedo, Mega Sharpedo, and Greninja. The Pokémon with the best defensive coverage are Aegislash and Heatran.

Answer 2

Offensively it can be the bolt beam combo ( thunderbolt and ice beam)
And if possible the shadow punch combo (made it up, but it is fighting and ghost, really good coverage)

Defensively. I'd say dark and ghost because it has no weaknesses (except for fairy, make sure to get a move that destroys fairy)
And also I'd say fire/steel, water/steel, fairy/steel, basically any dual type steel types,they have a lot of resistances!