My recomendation to you: No matter what model or size you get, get always a model with dedicated gpu.
For a 2009 model, look for the 9600 GT gpu, for a 2010 model, look for a Gforce 330M. This way you make sure to have a longer product live cycle and better balanced system. Since the damand on the used market for a 17' MBP is low compared to other models, you may watch out for an 17'er. They are the best machines anyways.