I'd say My Beautiful Dark Twisted Fantasy. Yes, it got rave reviews and what not, but impact wise and influence, that album came and went. G.O.O.D. Fridays, the Runaway video, and the hype surrounding the album was >>>>>> the album itself in terms of impact and influence. In comparison to every album that Kanye dropped before, MBDTF made the least amount of noise. It was one of those albums where the event >>>> than the album.
I'm not saying the album was wack, in fact it was a dope album, but being honest, that album didn't have moments like:
Jesus Walks
All Falls Down
Gold Digger
Diamonds Are Forever
Stronger
Heartless
^^^ All of those songs were huge and were "impact" records. When College Dropout dropped, there was a shift in Hip Hop towards the more social and political issues. Late Registration was more so Kanye's progression sonically. Graduation is really when the tides turned and it phased out the era that 50 helped bring back to the forefront. Then 808's influenced an artist like Drake.