United Abominations is a far superior album in almost every way.

Youthanasia is so... slow.

But, I will say, that even when I tried I could barely take in what was being said in the lyrics of Youthanasia, while on United Abominations it's almost impossible to ignore. Blame better mixing technology...

Either way, the recent claims that Megadeth "are back to their thrash roots" are at least true in this comparison.