I just find it annoying that people automatically go for Sylph when Sylvan is closer.
This. especially everyone parroting the "Sylveon is a flying type because Sylph is an air spirit hurr" thing. From looking around various forums, that and Sylveon's colours being somewhat reminiscent of the flying type gym leader were apparently the main reasons why people thought that.
People should focus on the names in other languages as well, as that is what really convinced me it's probably fairy. IIRC, it's French name is Nymphali. (and Feelinaria, german for fairy is Fee. I think, correct me if I'm wrong here. No, seriously XD)