That's an awfully open-ended question that can only be answered with "it depends". But a safe guess is that, assuming both machines are configured with similar hardware, the newer one will be faster.
That said, my advice for someone in your shoes is to replace the HD with an SSD and add RAM so you have at least 8GB. I did this on my mid-2010 21.5" and in casual usage it flies. It's nice to never see a beachball when using OS X. 🙂
Of course, this is also a much cheaper route to having a faster machine that will most likely last you another 2 or 3 years, and be able to keep up with the latest OS X upgrade. But it all depends on your use case.