K has outgrown her summer sleeveless undershirts so I need to pick up some more.

Do you prefer short-sleeved or sleeveless undershirts and why? I prefer sleeveless so they don't bunch up under L/S bodysuits and tops. But wondering if the little bit of short-sleeve is better for keeping them warm in the winter? But it might be extra thickness in the underarm area - especially under coats/jackets?