As much as I think the film itself is horribly flawed (yet endlessly watchable), my favourite fictional felines would be the cats from The Cat Returns. Muta, Baron, the Cat King (and even Haru at certain times): I can't really choose between all of them. Maybe it's just because if it comes on, I have to stop what I'm doing and watch it (and criticize all of the plot flaws like a grumpy old man), but I love me some Ghibli kitties.