Simerg - 1shot the ppl, but it's lotto because casting can be interrupted by cc
Urso - charge randomly. Once u get hit by charge, you will get knock back so it can interrupt our casting.
Pimen - help heals.
Ahella - Increase party member's physical dmg and does taunt. So it's good for pala burst and
sometimes your target will be changed to the this pet
Palconet - Increase party member's elemental dmg. Many of domi party has mage and scout in their group. so it's good for burst.
Adeline - send 1 ppl to ghostly world. While under this effect, that ppl is not counted as a player. So it's good for getting some progress.
It can be dispelled by mass dispell or martyr's protection.
Personally, I can't say which pet is better. All are up to situation.
If you fight stronger group and need miracle, Use simerg. If yourteam has mage and scout, use Palco.
If you need just few more sec progress, use Adeline.