Ok, first of all, I must admit that I don't have extensive experience with VTX. I just came across with VTX 3 times. I think that E15 have much more low end and it is very "in the face" sound and I in truth I don't like JBL sound, but VTX is much better then Vertecs.
I've never had an issue getting either rig to sound good. I prefer the sound of the VTX to the E15, but the rigging on the E15 is some of the best on the market right now.