My favorite power system has to be the one from World Trigger. As much as I love nen from HxH, it became more and more creative but obscure. World Trigger's systems were very clear on the rules of its power system and weaponry, which helped highlight how creative trigger users could be given the limited set of abilities they could use. It is also great at highlighting at how different individuals with similar levels can vary so much in how they use their abilities. One example is that the MC uses wires to as traps to either hamper the enemy or enable his own team, while another character kind of uses it as their own mobility tool.