Even if you read nothing(not that im suggesting it) you can learn alot by just taking 3 pets into PVP and see what your opponents have.
The ones that kick your butt probably have some good choices, and since you have most of the pets, you should be able to learn and develop similar successful teams.
Generally speaking, some good PVP pets are,
ones that can apply a Condition/debuff, then NUKE based on that Debuff/Condition
Example - Raven/Crow can call Darkness, then Nuke off Darkness with Nocturnal Strike
Other pets can Cause Burning then Nuke off Burning....Call Blizzard, then Nuke/Stun off Chilled Ect...
Then there is Synergy between teammates. Two or More pets that share a Bonus based on Debuffs/Buffs/Weather
Going back to Darkness, its the synergy between the pet that Calls it, and any other pet on your team that can also Nuke from it.
Like Ghostly Skull that can hammer you if Blinded. If your previous pet is killed/Stunned right after applying a Buff/Debuff/Condition, bringing in another pet that has an advantage based on that is nice.
When I mention Synergy between teammates, it's more of an advantage if the synergy spans different species. (Raven is Flying, Skull is Undead)