Really it just all depends on how relate-able/enjoyable/intriguing it makes the character. I've disliked and liked characters that are similar enough to each other, though, so I guess it comes down to the amount of characterization and if it's sufficient enough to sell the character, to me.
I adore Godai, Shouichi, and Ryoutarou, but I dislike Eiji.
I'm far more consistent on liking more aggressive and "edgier" riders. Love Yuuto, Terui, Ryo (Gills), and Hajime