I used Sony MDR-V6 (more or less identical predecessor to 7506) for years since the mid 80's. They are good reliable headphones, more or less an industry standard, and provide some isolation. Nice that they fold up relatively compactly for over-ear type closed-back phones. I still have them stored away somewhere although in need of new pads, primarily because all my other over-ears are open-backed.
Headphone preference is a very personal thing. The AKG K701 has too much treble peak for me, for example. Just not a good fit with my ear-canal resonance I suppose. I'm more of a Sennheiser house sound guy. The Mass-drop HD-6XX is what I'd look at if shopping for a replacement for my open-backed Senns today. Have been long curious about Beyer 880 and Hifiman HE-4XX but haven't found the chance to really give them a good listen.