Get a T or a W, they are fine, old-school corporate machines.

Carbon is the new, fashionable, Macbook-like device with soldered-on RAM, etc; likely from a different design culture. Its biggest upside is likely the hi-res screen.

I second going with the T line and would go as far to say that the T480 has a very modern feel to it. It is only slightly thicker than my old MBP 2013 retina 15 inch. (the thickness of the screen) I was expecting it to be much thicker and the fact that you can get 32 GB of RAM makes it feel like a very fast/responsive machine even with many applications running. Far more important in my opinion for a developer machine than having the screen of the Carbon.

There are high-res models in the T-series. I.e., available in both 1080p and 1440p, the latter just at the point where you can use it without High-DPI tech if you have normal 20/20 vision, if you have worse, you want less resolution (as you can't use the higher resolution anyway).

My vision is far from 20/20, and I have trouble discerning road signs at a distance, but I can see how pixels are square on most 24" FHD displays.

For development, a lot depends on the quality of font antialiasing and hinting, though; Linux used to provide superb font rendering in this regard.

I too don't have too good vision, but the 1080p 15" and the 2160p 39.5" at slighly higher distance are just at the point where I don't need High-DPI technology. Seeing pixels at 24" is not that hard. There are screens with significantly higher linear resolution.