Mosley was very tough to beat at lightweight and basically had to leave the division because it's biggest names wouldn't fight him.
Personally, I belive a fight between Mosley and Stevie Johnston in 1999 would have been a barnburner. Angel Manfredy might also have put up a good fight that year, but opted to fight Johnston instead (very good fight btw).
Anyway, Mosley was the kind of fighter who could rise to the grand occasion when necessary, Davis wasn't.
On top of that, I think a prime Mosley was a better all round fighter than Davis as well.
My pick would be Mosley by late TKO.
Davis had some good boxing skills, but like others have mentioned, not a good chin. Didn't have enough power to trouble Mosly either. Mosley by mid-late round ko.
I'd be in the Mosley camp here. Not sure Davis ever took things as serious as he could have. I think he had more gold in his mine, but wasn't the speelunkering type. Sort of like Naz but not as extreme in this regard.
