The Sony V6 and 7506 headphones have been a consumer and professional standard for more than 20 years because they're durable, comfortable, efficient, very reasonably priced, and sound great.
I've tried many headphones over the years, looking to upgrade, but always returned to the V6/7506. I've heard Grados that sounded great (not better), but I don't care for open-back headphones. I've owned Sennheiser HD580s but found the highs strident, and, again, I didn't care for the open back. AKG K240s sounded smooth and lively but lacked bass punch. The Sonys offered, to my ears, a better top-to-bottom balance than any of those.
Everyone's ears are different, and there's a pair of cans to suit them all. Many people love these Sonys, and have for a long time.