Let's see, shall we?
Armaldo
Pros
A high ATK of 125
Decent in terms of Physical Defense, with a respectable base DEF of 100
Rock/Bug typing, making it weak to 3 types only
Rock/Bug are both Physical types, so you can utilize its' STAB well
Cons
Very slow
Shallow movepool, not counting TMs, Tutors and Egg Moves
Barely has any Bug STAB, it being only Fury Cutter which isn't even the best
A little poor in terms of Defense, specially
Cradily
Pros
Respectable defensive stats with 97/107 respectively
Gets things like Solar Beam, Giga Drain and Earthquake through TMs and Egg
A somewhat wider movepool than Armaldo by a mile
Can be trained to a great multi-tank, maybe can be put up for a good use somewhere in the late-game competitive facilities
Cons
Nothing so special offensively, with its offensive stats 81/81 respectively
It is only special in terms of defensive stats, however defense is not much prioritized in-game, unfortunately
Grass/Rock isn't necessarily a bad typing, but It is clearly not the best either
Slower than Armaldo
Has a type overlap with your Cacturne
In this case, I recommend you to go with Armaldo. It can be a physical sweeping beast if trained properly, and I believe a proper speed training will also make up for that awful speed.
Armaldo @ Anything
Ability: Battle Armor
Recommended Nature/s: Adamant
- Ancient Power
- Fury Cutter
- Protect / Swords Dance
- Earthquake / Metal Claw / Brick Break
Hope this helps!