Depends on how you define producer...
The defenition?
Well a producer is in my defenition someone who is involved with every aspect of making the song.
I`m talking concept,ideas,vocal coaching,arranging etc, etc.
To me the greatest producer would be someone like Quincy Jones, David Axelrod, Lalo Schifrin or Bob James.
Someone who would be equally adapt with a 50 piece orchestra, as with a 3 musician/instrument ensemble.
A beat maker is something different. Someone like Marley Marl, 45 King or Prince Paul. Those were the early beat/sample manipulators that were pioneers in early electronic music(Read: Hip Hop).
The next level of beatmakers would be Premier who set the standard for chopped up loops, Pete Rock who mastered the art of layering samples or or Large Pro who has always been underrated.
And then there are the new Cats like Kanye West, Just Blaze, Nottz, Ayatollah and the list goes on and on...
But overall it all comes down to who`s sound/style you like the most.
And the person who has made my head nod the most times apart from Primo -has to be Alchemist.
But that`s just my opinion.
Ezion-DK.