Skarmory:
PROS:
- Spikes and stealth rocks
- Reliable recovery in roost
- Good flying STAB in brave bird
- High defense
- Taunt for stopping setup, and whirlwind for phazing those who have already setup
- Sturdy
CONS:
- Complete taunt fodder if you don't run brave bird
- Lower offensive stats
- Lower special defense
Celesteela:
PROS:
- Massive movepool, with moves like flamethrower and Seed Bomb
- Good steel stab
- Great defensive stats
- Leech seed
- Beast boost
- High stats in both defenses and offensives, as well as it's amazing movepool allow it to run a variety of sets
CONS:
- Worse utility movepool
- Slower
- Looks worse
In my opinion, celesteela is better. However, you can use whatever you wnt.
