Corsa D definitely. You get much more equipment (I don't think the C1 even has a rev counter), much more space, and it feels really well built. I've never heard of Vauxhalls being unreliable, but with modern cars reliability isn't that much of an issue any more, cars are very reliable now no matter what brand they are or what country they come from. It shouldn't cost that much more to insure or fill up, as it still has quite a small engine. It will also probably be quite a lot faster and better to drive than the C1 (998cc 3cyl engine, producing 67bhp), compared to the Corsa (1229cc 4cyl engine, producing 79bhp)