I have the PX550s. Use them as one of my 'daily drivers' on the commute to work. Very comfy, good isolation and sound nice. I came to the conclusion some time ago that I quite like Sennheisers sound. It's a bit 'v-shaped' from what I understand, so not super accurate, but more 'fun'. Have got some of their Momentum IEMs, also KEF M500, AudioTechnica open cans, Etymotic ER4s (since sold).