If everything elso was equal (maintenance records, etc) I would pick the 4 year old car. 4k difference is a lot, when buying a new car some people will fight tooth and nail for a $500 discount, so how come 4k is not a lot all of the sudden?
In this case both cars will require similar services performed due to mileage (breakes, coolant, ATF) and in my opinion the 4k would cover all of that and you would have plenty left for gas.
Of course this only makes sense from a financial point of view, you may want the 2 year old model for other reasons, such as refreshed body work, extra features, extra safety equipment, so factoring these in, the 4k difference may not be a lot after all.