Young is a better crosser, uses his pace better, is a better dribbler and seems to have a better shot. Walcott has got pace and that's pretty much it, he does get chances but he fluffs a fair few as well, no striker is perfect of course but he's not a good enough finisher to play up front.
I'd take Young over Walcott any time of the week, pretty sure Ferguson would as well. I said in the summer Young will be a real weapon for Man U as his pace will change their game back to how it ws when Ronaldo was around, it seems to have already happened, faster than even I thought.