I really enjoy running and playing Maze Rats. It is fast to get going, easy to explain, light enough to explain on the go but robust enough for a variety of situations that might come up.
It is my go to for one-shots, but I also like it for campaigns.
Seperately, I love the random tables. These alone are definitely worth paying for, and bring value to any game that you are playing. I use Maze Rats when I am prepping 5e, Dungeon World, and just about every other game I run.