In thinking of the ones listed here, Monk generally is the most complicated, at least in terms of decisionmaking. I chose this because I think most characters face a question of how best to use limited resources, but monks get a huge breadth of choice on how to use their resources.
In any given turn tou can spend a single ki point to achieve:
- Attack with one extra unarmed strike
- Stunning fist (for each individual hit)
This is just for base class too. If you go Kensai you get more decisions each turn. For subclasses, Elemental Monk and Kensai add the most tactical decisionmaking. Kensai at 3 gives you ranged abilities, but at the sacrifice of some power, or better defense at the sacrifice of power.
As a Monk you have to choose how to spend your ki points, because you can easily spend 6 ki points at level 6 upping your damage on weapon attacks, flurrying and stunning fist attempting on each hit. You can alternatively spend 1 ki point per turn dodging and using your weapon to provide AC. The options are wide and their optimal use is situational.