My dude, I been listening to rap all my lizzife...it's too many people dope at making beats to just Alc is top 20.
I'll take...
Premier
Timbaland
Quik
Battlecat
RZA
Dr. Dre + 1
Erick Sermon
The Ummah (as a collective)
Daz & Soopafly
Paul & Juicy
Nasheim & Carlos
The Neptunes (as a group, none of that "just Pharrell" garbage)
Ant Banks
T-Mixxx
Ski
D-Dot (who now that I think about it kinda did Alc 's style first)
Rick Rock
Bink
The Beatnuts
Rashad Smith (who is immensely slept-on)
That's 20 right there, and I ain't said Teddy Riley, Mannie Fresh, Easy Mo Bee, EZ Elpee,
Mr. Walt, Nottz, Hi-Tek, True Master, Wildstyle, Pimp C, Beats By The Pound, 1/2 Ounce,
DJ Pooh, Carl Mo, Organized Noize, Alchemist's teacher: DJ Muggs,
or chosen my favorite member of D.I.T.C. yet...