My Dad has an AUII Fairmont, Liquid Silver and Tickford 17's, and its one very nice looking car inside and out, goes very well too. We have never had a problem with it at all.
I can see the points of both - S1 AU's are fugly, except for some of the XR's (although Im not a fan of ones without a kit). Series II and III however, the only reason I wuold knock one back is because the resale value is low, because as you say people 'hate them'.
My only complaint with the AU's shape is that from inside, visibility is somewhat limited compared to my EF. The windscreen slopes down more, and it feels like you're sitting 'lower', so if you're a shoter person you may find driving an AU a little daunting at first. Well, thats my take on it anyway.
AUII onwards, the interiors are great. My only complaint withe Fairmont is the black interior gets very dirty very quickly, but it comes up a treat when its cleaned.
The headlights may be ugly, but goddamn do they put out some light!
Mechanically, I would say no car is free from its problems. The AU has a lot going for it though - better engine, no headgasket issue to worry about, better intake and much more fuel efficent too.
I think your old man's nuts to prefer an EA over an AU to be honest!