If I had to choose from one of these only I'd go for the 50-144hz 1080 model.
But in the real world there's no reason why I'd have too choose from one of these and although 3440x1440 would be my preferred resolution
a 55-75 hz working range is too small especially without LFC for when framerates go under 55.
That said it's hard to say without actually trying them out, There's other issues such as light bleed on IPS panels to take into account.
The bleed on the Asus Dominator I bought was terrible and along with how poor the working range I sent it back.
The 2560x1440 VA panel did not have bad light bleed but the resolution let it down so that got that sent back.
Then I had a stroke of good luck and found that a member here had put his Acer x34 on the members market ,
I grabbed it at it's asking price simply because I was able to ask questions about the monitors bleed and age first and there's nothing
better than hands on user info. I felt I could trust the OCUK member in question as he seemed genuine and had a good trust record,
It turned out to be the right call.
Sorry for going off topic,
Having briefly owned this 2560x1080 monitor:
https://www.overclockers.co.uk/acer...n-superwide-curved-led-monitor-mo-092-ac.html
and now owning this 3440x1440 monitor or something very similar:
https://www.overclockers.co.uk/acer...tra-wide-led-zeroframe-monitor-mo-11d-ac.html
The second monitor won hands down.
The resolution won't be an issue for a lot of people and if you are one of them the important thing to do is find a monitor with good Freesync stats ie: a 30-35 hz starting range and LFC support.
I think they are the most important features for a monitor that's going to be used for lot of gaming.