This isn't a useful question, because when it comes to characters, games can have varying levels of complexity, and can also focus on different things. So what makes a character "good" in one system may not be "good" in another. Plus, gaming groups will have their own preferences, which can also change over time.
For example, in Dungeon World you don't get much say in your character mechanically (you basically check a few boxes), you don't need a background to speak of, and the game is about dungeon crawling. I've played in Dungeon World games where players have both pitched really detailed backstories, or just filled in a name on a bond and answered a few questions before the dice started rolling.
Personally, a good Dungeon World character is one with a minimal background (only the necessary details, we can flesh things out later on assuming there is a later on) and primed to actually go on adventures, as opposed to, say, a fucking shopkeeper. I'm sure some will disagree, but since what a character is capable of and does is ultimately decided by their player, I think a better question is what makes for a good player.
Good players, for starters, don't show up for something like Dungeon World, then start bitching about how the game isn't about shit like helping to somehow uplift oppressed orcs. They don't hog the GM's attention and make the game all (or even mostly) about themselves. They don't claim that the only character they want to play in a 1st-level Dungeons & Dragons game is a half-dragon tiefling monk. They don't dismiss adventure hooks because the GM failed to sufficiently pander to them.
Good players play the game, and play well with the rest of the group. Instead of an obnoxious Lawful Stupid paladin threatening to kill any character that doesn't do what they want, or even frivolously consorts with things they don't like, good players find a reason to work with them anyway (of course other good players also don't deliberately attempt to goad said paladin into taking extreme action). Instead of a druid who refuses to leave her forest to go an adventure, a good player finds a reason (or just does so because that's the point of the fucking game).
A Sundered World: Player Fragments, the first supplement for A Sundered World, is finally out!
The Paladin is technically the sixth "core" class we've provided an alternative for. If you interested in an alternate class that isn't merely a half-assed reskin, check it out!
By fan demand, we've mashed all of our 10+ Treasure volumes into one big magic item book, making it cheaper and more convenient to buy in print (which you can now do).