Confession time: I am not overly enamored of "rules-lite" RPG systems. As long as the system is coherent and well-thought out, I prefer it when the system has rules for all sorts of things - from tactical combat to running chases to social encounters to falling damage and so forth. I like GURPS, I like D&D5E, I like Pathfinder 2E (although I haven't gotten a chance to try it as much as I'd like).
However, one thing that I want to be as simple as possible: NPC/monster creation. When I am the game master, I want to churn out the stats for enemies that the PCs can overcome as quickly as possible. Any time I spend on building NPC stat blocks is time I can't spend on working out fiendish adventure plots.
Here are a few examples of NPC creation in different systems:
Horribad: D&D 3.X, Pathfinder 1E. Too damn many derived values, templates, and so forth. Far too much math for far too little to show for it.
Bad: Exalted 1E/2E. NPCs have all the same stats as PCs, of which there are lots. Plus lots of charms with overly long texts, in the case of Exalted NPCs.
Decent: GURPS, D&D5E. The math isn't too complicated, and you can easily recycle and modify existing stat blocks - though you have to be careful so that these NPCs are balanced in a fight. Exalted 3E edges into this territory with their "Quick Character" concept - but they spoil it with insisting that "significant NPCs" should be built with all the same rules as player characters.
Good: Storypath System, Exalted Essence. I love how they boil down all skills to: "This dice pool is for what the character is good at, this is what the character is okay at, and this dice pool is when they have to do something they have no real competence at" - and the GM can define these however they like, and even improvise this. Then you have a very few other stats like Health and Defense, and you are set apart from a few special qualities! I've started running Scion very recently, and I am very impressed with this.
So, what other examples do you have of RPG systems that do NPC creation well - and which do it badly?
Mutants & Masterminds 3e (d20hero) can do anything; it's all the power of GURPS with a drop in the bucket as much math.
It also has NPC "minion" options where you basically don't have to worry about what their stats are beyond the very bare-bones because anything that successfully affects them takes them out of combat. They can be at any power level -- you could have something that is a world-boss-level threat to anybody who can't beat its basic defenses, but crumples like paper in the face of anybody with real power. I'm not sure why you ever would do that, but you could. AND you can even build them with merits like "Jack of All Trades" that give them that "they roll at basically this same modifier for everything" effect.
And if some NPC does eventually ascend to matter, you can generate them the same way you would a PC and it'll still take you an hour or less.