I've only heard the SVS PD12 once during my audition for the Axiom speakers. It sounded great, but I went ahead with the EP500 so I can get the 5% HT package discount.
Personally, I think both subs are great. My EP500 probably has a little bit smoother transition than the SVS that I heard and also a bit more detail, but then again it is most likely due to room size, system configuration, and positioning (I have it in front SVS was seated behind the seating area). I have to admit that the SVS has better look than the EP500 though if aesthetic is one of your buying criteria.
