Couple of things...
Saying that they've got a Merc AMG is like saying they've got a BMW M: We need more details as it's not a car in it's own right! Also, I'm going to guess that your old man isn't much of a corner lover but prefers his fun in straight lines which is why he likes the big V8 Mercs, as the performance of the 987 S really doesn't suck when you drive it hard through the twisties. Yes, it'll feel slower in a straight line as you need to work the gears really compared to the laziness that a torquey V8 brings to the party, but it's a bit harsh to say the Boxster sucks (even if it is your Dad's words!).
Also, we may be a Zed forum but I'm guessing we're all petrolheads first and foremost, so it really doesn't hurt to say when other cars our better than our own. We all had our reasons for picking the Zed over other comparable cars, but that doesn't mean we bought the quickest & nimblest & best looking car available to us. My car is much uglier than either the Boxster or the Cayman, is slower and handles worse out of the box, but it's got a touch more character IMHO and that's why it got my money. My previous car was quicker and better handling than any of the above, but sometimes you want something different in a car which is also possibly why your Dad likes his current steed.