Wow, thanks for the quick response everyone! This is really good because I'm trying to book my tickets tonight.

Ugh, Cathay Pacific's prices changed. Thanks for the heads up - you're right, I would not earn any AAdvantage miles going on Cathay because it is an M restricted class ticket.

So, now Cathay Pacific is a total of $127 more expensive for 2 people (I'm flying with a companion) than United, but I just found out (and confirmed with the reservations agent) that all 747-400s in Economy have no personal TVs. However, flying Cathay Pacific's flight is a red-eye and will allow us to arrive at 6 am on a Friday while the United flight arrived 6 pm on that same Friday, which gives us almost an extra day there.

Now my trade off is between gaining an extra day in Hong Kong but at the loss of United miles and e500s, and with an additional cost of $127. The personal TV and nicer food / service are perks now that I think about it and aren't as essential because I'm not traveling alone.

Also, I had looked up SQ as one of my first choices, but their prices were more expensive, so it only came down to these two airlines.