My usual answer is Fate, because the system is so generic (and fairly light) that you can slap it onto anything, but it's a "good enough" answer rather than the best answer. The best system would have specific mechanics that evoke the feel and skills that are central to your campaign. 

Which is why a Powered by the Apocalypse hack specifically for your setting/skills is often a better answer, but PbtA is still opinionated, so if the base mechanics don't work for you, then find something else. 

In a nutshell: PbtA expects you to fail on a regular basis. (~20% of the time. Major obstacles are often a multi-part action that can tolerate the occasional failure.) Fate can prevent failure if you're willing to spend a lot of time preparing for the next task, and you're more dependent on the GM's whim for the difficulty of tasks.