I go with player empathy to decide. I can’t enjoy a system if the player’s don’t like it.
I like Into the Odd because you’re up and running with rookie players in minutes. It could use a social mechanic, and I like to add in encumbrance based on their Strength score since the game is about looting and paying down debt.
I love Lady Blackbird for its skills-as-class system. A player can be literally anything and not be hindered by a class system.
Maze Rats I really did for all of the d36 tables it includes, though it’s really hard. It retains the PBtA 2d6 + STAT system but only 10+ are successes; there’s no recognition for partial success. Easy enough to add back in, but if someone picks it up and goes by RAW it can be tough. I feel bad for anyone who picks the mage class though, since they only get one spell per day. The other two classes get bonuses to all rolls in their domain.
Wildlings, a mostly forgotten John Harper RPG. You assign dice to your stats, from d4 to d12, and you’re trying to roll above a 3, with even higher rolls getting you bonus descriptors as to how you pull off the roll. I think as you gain harm you lose access to those descriptors one-by-one.