Honestly both are flawed though spell slots are the more flawed one. (Prepared) spell slots have some merits but are used wrong: they should be more an abstraction of material accessories than the bread and butter of a caster that’s expected to use their abilities frequently. Pathfinder 2e does spell slots right with its shit like daily free alchemical preparations, daily free talismans, etc even though it also does it wrong by doing it the D&D way too.

The issue with magic points is more a matter of implementation imo. It works better to have a flexible and interactive resource like that, though I think its most common implementation is bit too “pay X magic money for spell, you get Y magic money per rest (and maybe can drink magic money juice to refill it)” when it should be either a sort of short term limiter (you can do X amount per scene) or a sort of flexible tank that gets drained erratically when casting based on the strength of what’s being done (so small things can be outright free, while big things can burn you out for the time being, basically). Shadowrun’s approach of just treating magic as something that’s actively hurting you and which needs to be endured is also good.

There’s also something to be said for the way some systems merge magic and preternatural mundane effects into just different flavors of action, making them more narrative choices than strict mechanical ones. Sort of like how ICON handles its narrative play, where an action is ambiguously magical or mundane and how exactly it’s done depends on how the character narratively works (one example being traversing an obstacle, which could be a matter of a character successfully teleporting across it or some feet of agility, with both explanations being the same effect and the same roll).