I assume it would be more future-proof to go 4k, but I've also read some complaints regarding scaling issues, mostly.
Most basic everyday programs, webpages, and other visual user interactive things on a computer are made to be used with a 1366x768 resolution. Most laptops have a 15.6 inch screen.
A lot of professional software, professional software company webpages, and more enthusiast centered things are made to run on a screen that is 1920x1080 (1080p), and regular things also are tend ot be made to scale up to fit 1080p relatively well.
These laptops, are still, mostly 15.6 inches. So a item that was made to show up as an inch across on a 1366x768 screen. Will be seen physically as almost a half-inch item instead of a whole inch on a 1080p screen of the same physical size. However, 1080p isn't to much bigger, and things coming up as half their designed to be viewed at size is still very usable (again, most things have scailing built in them to try to adjust for this).
Now, 4k is, well consumer grade 4k and "UHD" is, 3840x2160 pixels. Professional use grade 4k screens are 4000x2160 (see where the name 4k comes from?).
That resolution is almost 4 times as high, and almost 4 times as wide as that "designed to be viewed at" resolution and screen size, and has twice as many pixels as the "designed to scale up to" resolution of 1080p. So things will come up, on that same 15.6 inch screen mind you, as 1/8th or, in the best scenario, 1/4th the size visually that they wee meant to be viewed at.
Windows has built in scaling you can use to automatically adjust things that come up, but generally speaking it's counterproductive for daily tasks.
However, it's an advantage if you're a photographer or video editor. Since your pictures are generally taken at extremely high resolutions. Resolutions much higher then either 1080p or 768. So if you want a full, more accurate, representation of what the picture really looks like. A 4k screen is extremely useful.
For video editing, video is typically filmed at a much higher resolution (usualy 4k) before being down-scaled to 1080p. Even if it's not being edited in 4k, having a screen with a higher resolution then 1080p means that you can have all of your editing tools on the screen around the edited video, without taking the video out of it's 1080p native viewing resolution to fit along side them.
4k everyday use is garbage right now, but if you really are buying the laptop for photo editing. Then getting one with it would be the obvious choice. As the advantage to view your photos in higher detail is much more important then your ease of use on Facebook.
That said, if at your price, you have to make a choice between a low RGB rated 4k screen, and a high rated RGB 1080p screen. I'd go with the 1080p one. As what's the point of being able to see more detail if the screen can't spit out the color to display that?