I'd say best:
1st-Ghost/Dark
2nd-Ghost/Normal
3rd-Dark/Ground

Based on inmmunities, resistances and importance of weaknesses (Ex: Ghost normal is worse because its weak to dark and dark has knock off, poison dark is weak to earthquake)

In the worst, I'm not quite sure, I'd say

1st-Ice/Steel
2nd-Grass/Ice
3rd-Grass/Bug

But what do YOU think? Just remember to consider not just resistances and weaknesses, but the importance of the type it is weak/resistant to