I love my ultrawide and it's only 2560x1080, much more immersive than 1080p and without the bezels of a triple monitor setup which I can't seem to block out.
That being said it depends on what games you play, like Downthesky says I can imagine that 3 monitors would be better for flight sims etc.
The 34 inchers are going to be even more immersive, but you might want to compare the actual visual quality of the monitors, things like Input Lag, contrast ratio I read a recent review of the LG in PC Format and they found that the input lag was noticeable by some but not others, and they felt that even though it was supposed to be native 8 bit with 10 bit dithering, it felt like 6-bit. At least at default settings. They were reviewing the Asus PG279Q ROG Swift at the same time so that may factor into their impressions.
I can only imagine the cheaper AOC to be even less focussed on these things that gamers find desirable, it's probably more designed for a workplace. It would be worth checking out a few comparisons first to see if it suits your needs.