You shouldnt think a set rotation, better think of it as priorities, cos in many scenarios u cant make a full rotation, and the shields of the target will sometimes be stacked top or left for example, which you should adapt to and use combos on the unshielded side.
1: Shieldslam
2: Guarddestroyer
3: Titanic smash/Overreach/Counterweight
4: Counterstrike
Shieldslam is the absolute highest aggrobuilder, so even if you have critbuff running from guarddestroyer, you should use shieldslam when its off cooldown. Dont use counterstrike if you dont have aggro, it doesnt generate enough aggro, and u wont benefit from its effects when trying to get aggro, when you have aggro on a meleehitting boss, you can squeeze it in there tho. You shouldnt do that thing when you're switching to polearm to do guard and bloody vengance, thats devastating for your aggro, first of all you dont need guard if you dont have aggro already.. second of all, bloody vengance is a very low threat combo, that also removes all built up damage stacks, so you're basically removing your damage for zero benefit.
Here's a video I just made with my rotation
https://www.youtube.com/watch?v=Xs6n...ture=youtu.be/