Of the classics, One Hundred and One Dalmatians is one I've always adored. It's not a 100% faithful adaptation of the novel (something I'd actually quite like to see some day), and the "English" accents veer on the side of Dick van Dyke, but it's still entertaining fun.
Of the more recent Pixar collaborations, I'll always have a soft spot for The Incredibles (mine and Sarah's first date movie), but Finding Nemo, WALL-E and Ratatouille are also enjoyable.
And as a child I loved Pete's Dragon and also enjoyed The Spaceman and King Arthur. And The Rescuers.
So yeah, my favourite is one of those. Don't ask me to choose...