The next time I fly C, I will surely try to do so in a 744 upper-deck, simply because it would be a new experience for me
But for regular trips in Y, I always prefer the newer jets, like the 777 or the A340...one thing that especially annoys me about the 747s is that (because of their huge mass), take-off is the most shaky out of any planes I've been on, it just feels nasty.
Short-haul, the A319/320/321s are quite comfy for intra-European segments, but it's nice that the Asian carriers like SQ choose to use a widebody jet even for the 2 hour flight from BKK to SIN