An excellent topic... I remember being 23 also... oh how long ago last year seems...

I'll break my "favorites" down like PremEx did (my list is UA biased):

Creature comfort-wise:
First: 747-400 (I haven't experienced the Suite yet so maybe this will change) I like the more secluded nature of the first cabin in the 747-400. i.e. everyone doesn't have to walk past you while boarding.
Business: 747-400 lower deck, specifically rows 5-7. Upper deck is cool, but frankly you give up too much space to be up there.
Economy: 767-300. Can't beat the 2-3-2 config.

If I have to be on a narrowbody, then it's the 727. But definitely not because of creature comforts. I just like the plane. In general, if I ran the world, all flights under two hours would be on 727s, 2-4 hours would be on A320s (yes, even an ol' Boeing fan like me can admit that in that category, Airbus has 'em beat), 4-6 hours on 767-300s, 6-10 hours on 777s, and greater than 10 hours on 747s.