RBL Lookups using Postfix or Spamassassin

[Anthony M Simonelli <a.simonelli@sbcglobal.net>]

I'm using Postfix with Amavisd-new, Spamassassin, etc.  I what to use
RBL lookups to stop spam, but I am unsure as to whether to have Postfix
perform the lookup or Spamassassin?  I know that if I enable it on
Postfix, those emails will be rejected and possibly legitimate emails as
well, but if I have Spamassassin perform it, my mail server will be
accepting a lot more email which will be more taxing on the server...

Your opinions and insight are greatly appreciated.