The last two digits of the serial # designate the model year. The 2 hatch Outfitter was built from 2006 to 2008 (model year). The 3 hatch version would be a 2009 model or newer. There are some significant differences:
1. The 2009 should have a "Click n Go" Drive locking system where the Drive drops in and automatically locks. Prior to that Hobie used a 'cam lock' system where the Drive is dropped in the well and there are two twist locks to hold it in place. The newer system is much more durable.
2. 2009 uses what is now called a "V-2 Drive". It is best identified by looking at how the fin masts (rods) are attached. V-2 uses brass inserts that the masts thread into. You can see this brass insert. For 2008 and older, the masts slide into plastic housing and are secured by a small Allenhead screw from the rear. The V-2 version is much more durable and maintenance - free. If both boats are otherwise sound, the '09 (verified visually and by serial #) would be favored due to these two design changes.
Accessories that come with the boats are also significant in terms of cost value. Three that I think are very important are 1. cart/wheels (let you launch and portage anywhere): 2. ST Turbofins (big performance enhancement); and 3. "large" or Sailing rudder for much better turning and low speed directional control. The replacement on these items combined would be about $300 new and I think they are all worth having to get the most out of your boat.
I would not discount the superior conditioning on the older boat. It's superior care out of the sun also has value!
Finally, make sure both boats are complete ( 2 seats, 2 paddles, 2 Drives). The Drives should operate well, not look abused and will reflect the care they got. Replacement parts are expensive for them!
Combine this information with any price flexibility of the sellers and your choice will be the right one! Welcome aboard!