I have used a pair of Superlux HD688Bs for a few years. They are super comfortable (once the original vinyl padding is replaced with velour), sound like they should cost at least 4x what they actually do, and have been completely reliable for me.
Recently I found myself needing more isolation, and I thought about going for DT770, but wound up with German Maestro GMP-8.35 D. After an initial few hours of getting used to closed-back headphones again, I find I really love them. There is indeed a lot more isolation than the semi-open HD688Bs, but I feel like I’m hearing more (or at least different) detail now too.