I think there are a few different ways to look at it: General notoriety (for good or bad reasons), general notoriety for positive reasons, and then most popular within the circle of people that actually follow female bodybuilding.
For general notoriety (good or bad) I think I see Natalya Trukhina (Kuznetsova) getting brought up by far the most simply due to her sheer size. A lot of people genuinely like her, but I think just as many almost see her as a "freak show" unfortunately.
For notoriety in the general public for good reasons, I see a lot of Julia Vins and Cindy Landolt. You see a lot of people posting stuff about how beautiful they are yet how they could also beat you up, etc., etc. You know, most likely girls to appear on internet lists that say something like "These chicks could kick your ass or outlift you", something along those lines.
I think for FBBs that are the most popular within the FBB community (ie. a site like this), I think Aleesha Young and Alina Popa stand out.