The teenager with a working class background in me says "get something cheap, you spoilt brat with rich parents". The father in me says "get something fairly new, safe and economical, you lucky boy to have parents who care enough and have the means to buy you something decent".
Don't get a powerful car, but, likewise don't get something that doesn't steer or brake very well as they can be death traps too.
Why do you need a big boot? If you don't need the space that often, maybe you're better off getting something smaller and a cheap trailer, roof racks or a pod.
Khaled