Maybe I relate too much to your Dad, but he may not want to overspend for something like a TV because he is thinking ahead to things like your upcoming college education.
I'm another who is torn between sets, although in my case it's between the Panasonic 1080 PZ700/750 and the Pioneer 5080/1150. (The other posters so far are very pro-Pioneer.) If your Dad really wants 1080 and has established a fairly firm budgetary limit, the Panasonic PZ700/750 is a great option. Their blacks won't match the Pioneers, but they are excellent sets nonetheless. The 1080 Pioneers may cost less than currently proposed when they finally arrive, but they will remain more costly than the Panasonics and well above your stated budget.
Everything that has been posted so far regarding distance vs resolution is great advice, but if someone has an emotional attachment to an idea, it's hard to persuade them to do something else, and they may never be happy if they do. While most of us here tend to downgrade resolution compared to contrast (although no one shoud get hung up on published contrast ratios), in both cases there is a juggling act. When is the point of diminishing returns reached? Different people will reach different conclusions.
Considering that the Panasonic 700's and Pioneer 5080's sell at comparable price points, it's largely a matter of contrast vs resolution, and proponents of either will argue that the other is beyond that point of diminishing returns on the virtue they value less. This is a value judgement, and because one side or the other shouts that they have found the "true religion" doesn't mean they have... at least for anyone other than themselves.
But you didn't want to hear about trade offs. You want to hear why Pioneer is better. I have a budget similar to yours and here are some reasons why I'm leaning toward the Pioneer vs the Panasonic:
Blacks are decidedly superior to any other brand (far better than in a movie theatre, in fact, but then so are Panasonic's, albeit to a lesser degree).
Better video processing. Most people won't notice, but a videophile will see a large number of subtle improvement that result in improved picture quality.
Convenience factors. 4 HDMI inputs vs 2/3. Removable speakers (I never use the built-in ones). A two inch narrower panel width. (I have space constrains, and it sounds like you might, too.)
Cachet. Okay, not really important to me, but it is to some. Like a Lexus, the Pioneer oozes quality and luxury. Panasonic is more a Toyota; solid, dependable, good quality, great value but not necessarily as blood stirring. (If your Dad doesn't drive a luxury car, forget this one.
But if your Dad decides to go with the Panasonic, don't be too disappointed. It's top notch. (Check out the raves by independent reviewers.) And you'll be able to buy your Pioneer in a few years when you are on your own. They'll be even better then. Probably cheaper, too.