Any year is fine. Note that some 3rd gen MDXs (not just 2014) have suffered from misaligned panels/doors so make sure you check the gaps on any particular one you get. You should do this anyway for any vehicle you buy.
Also keep in mind there have been infotainment bug (other than map) updates and some other TSBs to address things like a noisy rear end (clunking - my 2014 never had it) and a few other things so whichever one you get may have been updated or not but you still have some recourse since they're all under factory warranty as long as the mileage hasn't gone over the limit yet.
My 2014 has been a great vehicle and I'm glad I bought it. Just make sure you check out the specific vehicle thoroughly and pay attention to noises, etc. - i.e. don't just do a short test drive with the stereo cranked up like some people do (and some salespeople try to get away with).