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Bridgestone pretty much invented the ball-fitting concept a decade or so ago, ahead of the game as far as giving different players different options as far as figuring out which models provided them optimum launch angle and spin rates, and naturally different price levels. The e-series has been a very good seller for them over the years, designed more for the mid-level player.
I prefer the RXS over the RX, as I feel that it offers a tad more green-side spin, but other than that I personally can't detect any other noticeable difference in performance between the two. The original B330 didn't do anything for me... I felt it was a "heavy" ball, similar to the premium Nike balls I've tried over the years. Maybe they were too spinny for me. Who knows...