For a more detailed list of what the abreviations stand for, click here.

PvEG - Low (due to the time between stance, and limited stances)
PvEP - Medium
PvEB - High
PvER - High
PvEF - Medium
PvPS - High
PvPL - Medium

Standing Shot > Rifle: Though this is your first stance, you will find yourself using it for situations throughout the game.
PvEG PvEP PvEB PvPS

Aiming Shot > Pistol lvl 24: I don't think I would ever use this stance, since I find Freestyle more useful. However there is a large debate that Aiming Shot is better than even Double-gun Shot. Personally I don't agree, however the accuracy, attack speed and critical rate is tempting
PvEB PvPS

Freestyle Shot > Pistol lvl 24: I think it is a transitional skill before you get Duality. I would get it to level 8 as well as max out Quickshot so you don't waste duality points. If you are going to go with Enforcer, get Freestyle as well so you can switch back and forth.
PvEG PvPS

Kneeling Shot > Rifle lvl 24: Great single target damage and range, however it is sometimes annoying since while using sniper you can't move, and it also has a minimum attack range. This results in melee attackers having a great advantage over you.
PvEG PvEB PvER PvPS


Double-gun Shot > Pistol and Pistol lvl 36: Well rounded stance that has AoE and DPS. Many people argue that the accuracy is too low, however with the right equipment you can get 100 accuracy even while using quickshot.
PvEG PvEP PvEB PvER PvEF PvPS PvPL

Close Encounters > Bayonette lvl 100+: Not neccessarily the best skill though it is an Veteran skill. It does give you a helping hand with critical rate and blocking, however its skills don't make sense. None of them do AoE, and the attack on the single target isn't great. Sniper does a much better job. The only thing this has going for it are the effects: Knockdown, Stun and Critical Damage.
PvEB PvER PvPS