EDIT: I re read, if you are getting mkII akg 271s, then nevermind anything i said of them, it only applies to the previous versions.
The dt770s have been redesigned, and you have the older design like most of us. I would fo for the dt770s. AKG pleather pads on my 770s made them sound amazing, and i am trying to get jmoney pads.
You should really look into the AT m50. Efficient, extremely good build quality, the hf is like silk, and best of all, they isolate extremely well. unless you heqd is huge, i can't see clamping force being an issue.
out of every phone i have touched, the m50s still are in my top 5, i think. What sound you get for your money is incredible. The hd555/595s from sennheiser are good all rounders and have a ton of mods to turn them into a really comfey hd600 basically. They are open air, so no isolation. just like grados, you do not need to remove them to have a conversation.
Personally I w0uld get the the m50s, and also look at craigslist or ebay for a non mkII pair of 271a in the box.
Out of these i would take my k271Ses and go home an enjoy the fruits all the labor that went into building a respectable set of closed cans. These are not at all just k240Ses with closed backs. The k271k not the mark II, but the original 271s is easy to find,
I got mine basically new in box from craigslist seller.
Once i gently oiled the pleather, was sure the mute switch was working without an audible difference, i don't remove the feature because it can come in handy. They are very simple to EQ, and can dip down into those lower octaves with power as well as the snap of a fast percussion attack. They are nothing like tthe k240s The k240 S and newer sound like music through a musty sock. Not so with the 271s. my wife can even tell the difference.
I can speak for most of the phones in this shootout. The beyer dt770s and the akg 271s are a really good choice.
The Shures are waaaaaay to revealing for listening for enjoyment,. By this i mean their going to highlight every problem with the recording and also add a bit of siblince. I much much much prefer the AT m50s over the shure 440s or 840s. i have kept them if i want to have a clean, flat, without personality, audio device to hear music i may produce from time to time. They are more accurate than most nearfield monitors, just not in the sound staging, you still need speakers to handle that one. Although, separation of instruments is most certainly there, as well as the take the headphones off and look around because you didn't know if it was in the recording or real life.
The M50s can do it without shredding your ears. (for the price, they are hard to beat, honestly. I should sit down with my k271s and m50s and see once and for all, which is the most musical, yet accurate. I have DT880s, but they are twice the price or more, however, they do not win in every instance.) What you can get for your money today can floor you if you know where to look.