Do you really have to have you parents aproval? Hell my dad was pissed when I bought a $22,000 car with 14,000 miles through ebay and had to drive it up, but I did what I wanted and everything has worked out.
Since they are afraid of you buying used have a fellow VX owner here on the forums test drive the one you are looking at to make sure its up to par.
Not sure about the ac thing but I doubt ones much better than the other. Just look for the best VX in your price range. As for the climate control its not a big deal to turn down the heat when its hot is it? I mean hasn't every other car you have owned been like this... I have it and like beeing able to set the temp I want, but its nothing that would sway me to buy one over the other, unless they were exactly the same milage/condition/price.