I prefer the FXT90 overall by quite a bit... but when owned the EPH-100s, preferred them for psytrance. Their in-head, non fatiguing, warm albeit detailed sig made them perfect for swirling synaptic squelches and snarling acidic rhythms.
I don't generally listen to guitar music light enough to be called rock, but would agree with Shane that the FXT90 truly excels with distorted guitars. They portray crunch in a way the Yams can only dream of. I'd also say (though many may disagree) that the the JVCs are overall more versatile and can pull off a wider range of genres, and whilst they can't pull off psytrance quite as well as the Yams, they certainly don't do it an injustice. In fact, their forward and assertive presentation makes psytrance a very exciting and engaging listen.
The EPH do isolate better, and are more comfortable, but I'm never left wanting with the JVCs. I found the EPH-100s better for passive listening (in bed, or relaxing in the evening) and the FXT90s very good for active listening (running, cycling).