I think Neville is weirder. He's awkward and annoying. Luna is just funny because she knows about things that no one else knows about and she trys to stand out and be herself in a crowd. xP
Luna is definitely the weirder of the two. She believes in creatures and theories which no one else - save her father and the occasional Quibbler fan- does, and generally acts and dresses a bit weird. But that's just what makes her wonderful and makes us love her.