Positive is supposed to be the positive one. It makes sense. However, he actually has a very short temper, and a habit of sparking off fights. Very, very protective of his computer, which he loves dearly, but that doesn't stop him kicking seven shades of the proverbial out of it when it goes wrong.
Negative is supposed, following the flawed logic of this comic, to be the bad one. You know, evil, dark side using son of a female dog. In actuallity, he doesn't really care. Very laid back and apathetic towards most things. He knows Pos loves his computer dearly and therefore does everything in his power to steal it from him.
Audrey III is the pair's carnivorous plant, despite the fact that it has no apparent jaws or meat-digesting-capable internal organs. That doesn't stop it from trying, though.