I'm glad someone already advocated for flat, but I'll advocate for curved. I found that with even a 27 inch non ultrawide flat if you're too close the screen feels like it's curving the opposite way (obviously isn't but that's the experience). What's key here is how close you sit to the monitor. Flat screens are great from a distance. Curved is great for immersion, but you need to sit in a sweet spot to fully take advantage.
I don't end up doing any of my coding full screen so that's not any issue for me. neither an issue for any design work personally even if I full screen my work.