Only pick 1album!. I think the choice has to be made from:-

1999
Purple Rain
ATWIAD
Parade
SOTT
LOVESEXY
BATMAN OST
Graffitti Bridge [yes it did have some good B's on there!]
DIAMONDS & PEARLS.

For me it has to be Parade, seems to be the Revolution at their musical peak, W&L and P seemed to create and play extended 12" and B sides that had the most gorgeous, lush melodies from what was perhaps an underdeveloped Album. There really needed to be a remix of Girls & Boys though!.

Lovesexy remixes [aside from the sheer genius of Heaven Parts 1,2 &3] were pretty boring. SOTT package was pretty amazing too, especially letting Eric and Atlanta some free expression.

ATWIAD