PVCs: they feel as if I'm getting kicked in the chest and I'm unable to breathe when they're happening.
PACs: they don't affect my ability to breathe. They feel like light tapping.
For me it varies greatly. Sometimes my ectopic beats feel like a premature normal beat followed by a pause. Sometimes it's just a pause. Sometimes it's a tickle or a pressure sensation in my chest or throat. Sometimes it feels like a kick or punch to the chest, or a wringing of the heart.