I was there for both, but even though i know the prem is far more important as a trophy, i've found that the FA Cup win meant more to me (didn't expect it to, only realised it in the days after the prem win). It must just be that it was the first proper trophy i'd seen us win in my lifetime, it was the start of the change, it was amazing. On a personal level it hit me more. And as a kid i never expected us to win the league (!) but i had hopes for the fa cup every single year and used to cry so much when i was really little each year when we lost! But here we were - actually winning it! It was like my childhood coming true at the age of 36!! :)
Not saying the Prem isn't amazing, and of course it's harder to win, i think i just felt the actual trophy giving was an anti climax from where i was (couldn't see a thing, and the 2 blokes in front stood on their seats even though no one else in front of them did so it's not like they did it to see better, so my pensioner mum couldn't see - neither could i really!), and for some weird reason i've let that slightly taint it for me! Yeah, i'm weird ;)
Of course both are so so special, and yep, i can't quite believe we've won the prem! I saw some kids city pjs in marks today, and thought how they never had them when i was a kid, then i remembered oh yeah we're champions!!!!! It still keeps sinking in - that we are THE team. It's weird! Until it finally sinks in fully, it's still the Cup win for me. I still keep thinking i will wake up from this life on mars coma and someone will tell me Billy McNeill has just pissed off to Villa ;)