If you can swing it, go for a 2010. Prior to that was the day of the C2D chip. The first generation iX chips are significantly better - my 2.4 i5 chip in my 2010 MBP performed 25-50% better than my old 3.06 C2D for my major tasks. Also, starting with the late 2009 models, the screens where much better - 60% color gamut increase. Lastly, if you want to get a few years out of it, best to not get something that is already 4 years old. You'll be replacing low life, pun intended, batteries, and not sure what year they came out with the trackpad, I think 2009.
As far as ebay, look for sellers that have been there for years, sold a lot, and have near perfect review scores. I sold 3 older macs on ebay - great place to buy but hard on the seller due to fees.
Also, once the 2012's come out there may be a price drop on the more recent MBP as refurbs at the apple site. I know mine took a tumble in price drop once the 2011's came out. Here's a link to the refurb store
http://store.apple.com/us/browse/home/specialdeals/mac