Bikes which have put the biggest smiles on my face:
1) 1980s Puch Alpine - more because it was my first ever road bike than because it was a great bike, I suspect. Wish I still had it now.
2) 1960s Cinelli Riviera - easily the nicest bike I've ever owned, this one certainly has that wow factor in spades. Really shoots forward when you power down on the pedals and the only bike I feel happy doing fast downhill cornering on, plus it stays lovely and comfy on longer 4hrs+ rides.
3) 1930s Raleigh Roadster - lovely ride quality and heaps of character. Forces you to go a bit slower and the super-upright position is perfect for relaxing potters through the countryside (and I'm not plagued by any thoughts of cadence, average speeds etc etc)
4) 1990s Marin Hawk Hill - again not the greatest of bikes but MTB'ing is a real breath of fresh air for me, sheer silly fun
@mustang1 has got it right, it's the type of riding rather than the bike that makes the ride, for me.
However, I also always wonder what makes some of the old ten speeds such fantastic bikes too. Can't put my finger on it, but there is definitely something there, and evidently a lot of others agree!