This depends on your room, your listening habits, how loud you like to set your sub, placement, etc...
I've owned the 350v1, ep500, 2 ep350v3s (currently, and and ep600 (currently). The new 350 blows away the orginial king of the hill 350 from a few years back, and in some respects rivals the 500. It won't play as low or as loud as the 500 by design, but the new 300 watt amp they have gone to is killer for the price.
Below is the thread Alan started when the 350v3 came out, comparing it to the 500 and other brand subs.
http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Number=179265#Post179265
