You've got a point about modern day game's box art being less creative. I mean just look at Metal Gear Solid.
It's a shame too. And with the way the worlds going, box art isn't going to be around for much longer anyway.
And as for my favorite box art. I've never really given it much thought. Off the top of my head, I've always like the Zelda and Pokemon game's box art.
Twilight Princess and
Pokemon Gold/Silver spring to mind. And I also love
Dragon Quest VIII's box art.