The more points you score, the more new ships you can unlock. Each ship has slightly different traits. The larger ship is easier to control, but you won't be able to spin as quickly. The smaller ships can spin a lot more quickly, but it is a lot easier to lose control of them. Overall, though, the smaller ships are easier to set a high score with. Not only is the flipping the cause of this, but with a smaller ship, you're also a smaller target. It's a lot easier to escape from a meteor. If you are using a larger ship, you have more ship to get out of the way of the meteor.