I highly recommend the Dell, but I have no experience with the other two. The colour is fantastic, you can customize your workspace and much more. I haven't started taking advantage of the display manager software yet, but I've read that it's pretty nifty for creating custom profiles. It looks fantastic, and the ergonomics is great compared to the other two as far as I can tell. For me, the Dell stand makes a lot of difference. OSD is easy to navigate. I was planning to write a more complete review (or do a youtube review) when I had used it for a month or so, but I'm not sure if I will.
If I were you, I'd spend some time reading and watching every review and unpacking/stream/whatever you can find on the intarwebs before you decide, since you can't see the monitors in person. I think that the curve is absolutely amazing, but as @ShadowCaptain states, it's very much a matter of personal preference I think. Imo, the curvature really compliments the size.