My top 2 are Lil Wayne and Waka Flocka Flame. Wayne speaks for himself. He is one of the best to ever do it and has like 20 or 30 mixtapes. I heard T-Wayne for the first time recently and it reminded me how good Wayne is.

Waka is different though. Guy doesn't rap like Wayne, guy gets you hyped. He only had 3 albums but almost as many mixtapes as Wayne. Also worth noting is that while his last album was in 2012, but he has dropped at least 10 mixtapes since then. He doesn't need the money, he just loves making tapes. A surprising amount of them are on Spotify too if you have never given them a listen. I won't pretend they are all amazing, but I recommend I Can't Rap and Twin Towers. Again, don't expect lyrical rap. Waka is for when you need to get unreasonably hype.

Honorable Mention to Nicki Minaj. She is mostly known for her pop-rap stuff, but she raps hard on Sucka Free,

Mixtape era Canibus. You should also revisit the DJ Tony Touch 50 mixtapes that featured freestyles from the emcees of that era.

Papoose

Peedi Crakk, Saigon or Childish Gambino.

Lupe's mixtapes were great. Also 50 cent's mixtape run with power of the dollar etc.