One or the other? Hmm. Tough one because I love them both.
I'll end up betraying my air cooled brothers (and my deceased dad) but I'd have to say I'd take the '00 over the '84. Take nothing away from the '84 though. It feels so "old-school" and I just love getting in, dropping the top, and driving it while listening to that totally unique air-cooled growl.
The nice thing about the 996 is I can drive it every day and know it'll be quiet, reliable, warm (or cool), dry (no leaks) and safe, but that when I want performance and a nice growl from the exhaust, it's there in spades, just waiting to be tapped.