Let's take a look at Cradily's Special Attack...
Special Attack: 81
It has the same base stat as its Attack, and Infestation...?
Base Power: 20
It's not that much, but Block...?
Base Power: IT DOESN'T EVEN HAVE ONE!!!
Really? Trapping your opponents is one thing, but attacking matters too.
So Infestation or Block?
I would definitely go for Infestation, because not only does trap your opponent, the opponent also receives damage.
Who would expect Infestation on Cradily? Block can be expected (sort of).