Menenius is a smooth-talker, while Coriolanus is way more comfortable with a sword than a, well, pen. Menenius understands that you have to lie and manipulate to be a successful politician. (Remember how he pacifies the rioting Citizens with a little fable in the opening scene?) Not Coriolanus. The guy just can't keep his big, pleb-hating mouth shut.
As a domineering mom, Volumnia isn't afraid to speak her mind. She's aggressive, loves warfare, and embraces Rome's stereotypically masculine values (read: violence). Her mild mannered daughter-in-law, on the other hand, rarely speaks, never criticizes Coriolanus, and hates war. She's the only character in this play that doesn't think Rome's macho, warrior culture is awesome, and she's also the only one we kind of like.