I think the w4 is good for everything actually as long as it suits your preferences. The biggest thing is the warmth as it probably is one of the warmest iem I have ever owned. However I may be one of the few here at headfi that doesn't believe in genre specific headphones. The UE900 is just bad imo.
Yea, as I think about it...in 10 years on HF....UE900 might be the biggest dissapointment I have come across.