What a fantastic, gripping review thread. Two of my current sets were reviewed.
I discovered the Panasonic HTX7s after being lured in by their styling. I wasn't blown away initially, as I found them quite bright for my liking, but burn-in has definitely helped them become my 'serious' listening pair - I'm not brave enough to buy serious headphones as I expect it would be a slippery slope to bankruptcy! They work with all genres, from Brostep to Blues, to metal to pop and I love listening to a core set of around 100 songs that really shine with this pair. One peculiarity I've noticed is, from 'cold', where I've not listened to them for a few weeks, the warmer sound is absent and for around 30-45 minutes they sound a little reserved, but then they warm up and their qualities come back. I most recently noticed this last night, when listening to around 40 songs, the first half were a little underwhelming and then it all clicked and the second half of my listening was bliss.
My other pair are the Sony XB500. Using the older iPod Dock with the line out, the default sound level is a lot higher with this headphone than the Panasonic, so they really are only for listening to bassy music when I'm in the mood - for rock and metal I think they are awful. The way they push bass through your head and sub-bass feelings in your extremities is a lot of fun, but they are a luxury purchase, in the sense that if you could only afford one pair, you'd be letting yourself down by only having these.