List of self-known good Allies for attack strength or speed:

Anti-Snail: Attacks every four seconds for a decent amount of damage. ~62500 DV
Prehistoric?: All of the cyborg prehistoric mobs attack for an incredible amount of damage every seventeen seconds. ~37059 DV
Enraged Bomb: Attacks ONCE A MINUTE, but insanely powerfully. ~32500 DV
Giant Rat: Two attack types for high combined damage. ~23123 DV
Flame Cactus: EXACTLY the same as a Giant Rat. ~23123 DV
Sand Abuser: Two attack types for high combined damage. ~21269 DV
Gold/Platinum Jelly: Attacks every 23 seconds. ~13044 DV
Pirate Gem: Attacks every ten seconds. ~10500 DV

DV=Damage Value, higher is better.
Damage Value calculated based on 100,000 as a constant in testing how much damage is done per second.
When calculating multiple attacks, use the following formula:
(100,000 * A.BC / d) + (100,000 * X.YZ / w)
Here's how it would work if it were the Giant Rat:
(100,000 * 2.6 / 23) + (100,000 * 1.3 / 11)