Depends entirely on the game. Either can work fine if the rest of the game is designed in a way that fits them. The Witcher 3's story would have to be completely redesigned if you make your own custom Witcher character, as Witcher 3's story is entirely bound up in Geralt's personal relationships and wouldn't work with any other character. Different types of stories will lend themselves to different types of player characters, and it just depends what type of story the devs are trying to tell; one type is not inherently superior to the other.