There are many small-to-medium differences between Python and Ruby, but in my experiences, no one actually chooses one language over the other because of these differences. When you ask someone, "Why do you prefer Ruby over Python?" or vice-versa, everyone has their favorite differences to talk about, but often, the choice is actually made before enough familiarity with both languages is established to be aware of those differences. Most people choose between the two based on je ne sais quoi, rather than an objective comparison of the differences.

More succinctly: "Ugh! Python? I hate the idea of syntactic whitespace," and "Ugh! Ruby? I have the idea of using @ for instance variables," are both cursory judgments that mask deeper preferential foundations therein.