Personally, I would take a Boxster S over a Caymen S. The reason being is that I love having a drop top and it would be a requirement for me. I've never checked, but what are prices typically like on used two year old Boxsters?
Boxsters hold their value quite well. A quick search on AutoTrader finds prices for 2009 - 2011 models between $55,000 and $80,000 depending on trim, options, and mileage.
This one is a 2009 with 10,000km is only $43,000 - seems like a stupidly good deal, comparatively.
Outstanding cars, though. I'd love a Boxster one day...