There's no question in my mind that the 2e DMG is utterly useless. It's crap; it's tripe; it's worthless drivel. (All IMHO, but the 2e DMG is one of the very few D&D books that I keep on my Shelf of Shame, and I almost never used it during 2e, swapping the 1e DMG in instead.)
The 1e DMG, on the other hand, is amazing.
The 1e MM2 lacks a lot of classic monsters, though many others came from it. I'd get the 2e MM over it, though- it's just so... damn... complete! It has an incredible array of monsters.
As for the PH, the 2e PH is far less flavorful. The 1e version wins for Gygaxian prose, but the 2e version has the best specialty priest rules D&D has ever had- if the DM is willing to spend the effort for his campaign.
I'd go 1e PH, 1e DMG and 2e MM.