I dunno (about Utd having a better defence/forward line).
De Gea, whilst admittedly a good keeper, has looked distinctly pish at points this season. Rio is on a downward slope, and quite a steep one at that. Vidic, whilst quality is currently injured and thus useless. Evra has been regressing for two or three years. Raphael is very impetuious. Johnny Evans has actually improved with regular games, but is still no more than a very good PL player. Smalling and Jones are both good players with big futures ahead of them but Fergy bought them for 3 years time not now (he even admitted as much).
As for Utd's forwards, Rooney is the definition of a form player. When he's hot, he's unplayable. When he's not he's a waste of space. Wellbeck is very similar to Evans, a very good PL player but I suspect the top European defenders would be rubbing their hands at the thought of marking him. Hernandez looks good, but I get the impression Fergy isn't 100% sure about him yet. Berbatov has been criminally under played but we all know Fergy doesn't trust him. Owen's career ended when he left Real. Oh and do I need to comment on Bebe!?
On balance, I'd probably take Spuds squad, but I'd want cover at CB and possibly an extra RB as I'm not sure Walker is anything other than a new Glen Johnson.