I'm a pretty big fan of opposed d6 or d12 dice pools, with a success threshold and comparing highest die to opponents highest. This gives you degree of success, which works for damage, but also great for conditions that may be transient and easy to remove, or very difficult to overcome.
It's fairly swingy while giving someone who has an extra die or two a big advantage, which fits how I want superhero fights to go. I usually use d12s when I run Planetary or Cosmic tier games, mostly just because.
Challenges aren't opposed (cause there is no opponent), they just require a number of basic successes to overcome.
This is the basics of how the "unleashed engine" that powers my Simple Superheroes game. I use a variant of it for a "Dungeons Unleashed" campaign I am running now, (d12s but fewer dice usually, and I'm more likely to adjust the success threshold).
Otherwise - d100 is intuitive and
Diceless as in Amber is great, am I allowed to say that in a thread discussing dice mechanics
?