Before I go into it, I'd like to clear by no means I'm starting a 4K vs UltraWide rant, just my personal opinion and what I'm looking forward to in the upcoming tech.
I jumped on UltraWide ever since the early models from LG which came in 2560 x 1080, moved from there to 3440 x 1440 and in the early days, it was a huge pain to get games to work, but it got better later on, but still wasn't perfect.
And then I jumped on 4K when the very first models from Samsung became available for consumers, and have upgraded multiple models since and been using 4K G-Sync for the past few years now, next upgrade is 4K G-Sync HDR 144Hz from ASUS alongside the recently announced BFGD from NVIDIA later this year.
So, coming from intense amount of experience in both of these, I personally prefer 4K among UltraWide myself. Albeit, it is more taxing on GPUs and some games still can't do 4K60 maxed out, but any half decent optimized game has been doing 4K60 maxed out (except AA, not needed in 4K) on a single 1080, I seldom use my 1080 Ti for it as well. Not to mention, 4K panel is G-Sync so even if it can't maintain 4K60, anywhere from 40fps and above with G-Sync makes it appear just as smooth as 4K60, granted it won't give you the native 4K60 experience, but if you have used G-Sync, you'll know what I'm talking about when I say the 'smoothness' is stabilized because of it. So, even if your GPU can't handle 4K60, G-Sync is God-sent for that. I retired out of my UltraWide days long ago after jumping into 4K and never looked back, it was still being used simultaneously (no thanks to Windows and its crappy scaling for multiple monitors with different resolution), I never really bothered to game on it again. From productivity POV as well, I preferred 4K over UltraWide myself but YMMV.
With all that said ...
I am really looking forward to 4K UltraWide like the one announced from LG (falsely being advertised as 5K UltraWide despite being 2160p only), I personally prefer more real estate to work with, whether be it in game or productivity than simple UltraWide. I'd rather have more screen on top and bottom as well, not just on sides. But this 4K UltraWide with upcoming consumer NVIDIA GPUs (Volta/Ampere) should be able to handle 4K60 just fine. Obviously I'll enjoy fps games on that 4K 144Hz more, but in indie titles and games like Life is Strange for example, anything from Telltale and the likes, I'd enjoy it much more on a higher resolution than just UltraWide.
Zabojnik, beautiful screenshot from Zelda, fam. Shared it with a few buddies of mine.