carbon is stronger as in stiffer but it will only hold so much stress before it gives and then snaps, resulting in an expensive repair. Plastic will take also only so much stress but it will bend and flex a lot more than carbon so it is harder to break. Also if you put your plastic parts in boiling water for a few minutes it will make them even more flexy so you will break them even less. Rule of thumb if you have a lot of money and do a lot of racing and you are an experienced driver that doesn't crash much and want the lightest parts go carbon, if you just bash and sometimes crash go plastic.