First thing you should gauge is the frequency of certain class types your facing. Then build a team that counters much as possible while being hard to counter yourself.
A vast majority of PVP teams currently contain a Humanoid. Anubisath Idols are heavy used, many still cling to there Kun-Lai Runts and Imps.
With Christmas now here you can expect the number of people rolling Humanoids to spike even more, with the new Rotten Little Helper and old Winter Helper.
A alarming amount of people are also using Unborn Val'kyr.
To build a high percentage winning team it should be designed around countering Humanoids and a answer to the Val'kyr. Awhile ago i designed a team to do just that which i'll share with you.
This team is : Macabre Marionette (undead) Infested Bear Cub (undead) Spineclaw Crab (aquatic) Current Record 49-5-3
One of the main threats to this team is Critters which is the least used in PVP, if you do encounter one abilities Rip & Maul are strong versus Critter.
If your opponent has Unborn Val'kyr 95% of the time they start with it to Curse of Doom then Haunt...Always start your Crab first and counter with Rip then Blood in the Water which will eat more then half it's health before haunting. Your crab will take less then 200 damage from Haunt and 360 from Curse which all can be erased from it's 550 Healing Wave.
Other strong teams is : Crow (flying) Spectral Porcupette (magic) Gooey Sha-ling (elemental) - Darkness.
Murkalot (humanoid) Blackfuse Bombling (mechanical) Spawn of G'nathus (aquatic) - Heavy Hits.
Fiendish Imp (humanoid) Fiendish Imp (humanoid) Blossoming Ancient (elemental) - Strong heal dots.
Ask if you got questions.