Art of Storytellin' 1 & 2, Chonkyfire, Liberation, SpottieOttie, Rosa Parks -- these tracks are pure gold. If the album didn't have the song "Mamacita" on it, it would be perfection.
Runners up would be Enter the Wu Tang, Me Against the World/All Eyez on Me, Straight Outta Compton, and any early album by Ice Cube.
I've found a lot of people put Nas - Illmatic at the top. I'll have to revisit that album as I haven't heard it in years.
This one changed how I thought about music as something that could artfully express anger, alienation, ambition, and sexuality. Blew my doors completely off.
This one changed how I thought about rap and electronic music in general. Very hard to beat and not encumbered with a bunch of gangsta ********.
These got me excited about rap and its possibilities as a format for dark, apocalyptic sounds. These recordings often present ideas and arrangements that translate into interesting rock music. Very unusual.
I only own two rap albums, Life After Death and Ready to Die, therefore they are in a deadlock for best rap album ever. That they were the product of the greatest rapper ever solidifies my argument. I hate rap, but I love Biggie. Go figure.
I'm old school, so PE's "It Takes A Nation Of Millions To Hold Us Back" is probably the answer. Although I think "Straight Outta Compton" was more influential.