Steve,
It's upto you which car you want to buy but as a new driver you should aim for cars which reside in the lower car insurance groups of 1-5. This will make it easier for you to get cheaper car insurance quotes. To start off, have a look at the guide for cheap cars to insure for new drivers which will give you an idea of what to go for. You can check how much each of the cars listed there are going to cost you in premiums by comparing quotes from different insurers (a car comparison site will come in handy here).
It is best if you take the plunge and take out a car insurance policy in your own name rather than going on your parent's insurance. If you do decide to become a named driver on your parent's policy, then you may find it better to go with an insurer who will give you no claims discount whilst being a named driver so that you don't have to start right from the beginning when you get insurance in your own name.