Ultra wide is like having two screens, when splitting windows left and right, though I think two monitors is better for work, as you can put one as the primary and one off to the side, you don't want to be looking sideways when working on code.
When I was reading a lot of code I didn't write, the 4k was the best, as it had a lot of vertical space.
The ultra wide I bought for games (it's 120hz).
I'm about to start a new gig and I'll run 2x23.8" 1080p for that.
Phillips make decent 4k screens at 40" and 43" for the money, but they are glossy so no good if you have glare problems.
The nicest screens overall for work I find are the Dell ultra sharp line. They are premium in price but side by side to a cheaper monitor and you can see why!
I have a 27" ultra sharp that is about 8 years old and is still fantastic compared to most mid range monitors, it's worth the investment. 1x 27" is nice, 2x 23.8" is nice.
Samsung make good ultra wides for work, and they make some ultra ultra wides too!