I'd go with the new much faster 13" MBP over a 2008 era machine. The one thing that doesn't make sense is what's your budget? There's no way you a 2008 laptop is going for a 13" MBP price.
The other factor is how important is it for the larger screen. That is you have not mentioned your usage needs and its difficult to discern how each model best fits that need. All things being equal, I'd say the new model beats out the 5 year old laptop any day.