I've gone from an Xono, to the Herron VPTPH-2A, then for a very short time to the XP-15 before settling on the Pass XP-17. In my system, which is all Pass with a Spiral Groove front end and My Sonic cart, it is super duper nice.
I liked the Herron but it wasn't in any way better than the XP-17. It wasn't really close. In. My. System.
However, if I had a Herron pre and or those awesome mono blocks, it may be a different story.