I think David was a bit superior. Both in terms of career and peak level.
I think Haas vs Davydenko would be a good comparison.
In terms of career, it'd be a pretty pointless comparison.
Davydenko WTF/TMC winner > Haas hasn't even played in the year-end event ever
Davydenko 3 Masters 1000 > Haas 1
21 titles > 13
Also far more stability as a top player.
I suppose we could argue about peak level, but career wise Davydenko has done much, much better. Haas does have a Olympic silver medal going for him though, forgot that.