I am a heavy user of Cellular connectivity with my iPad Pro. It is my go to device on the road and while travelling, open it up and it just works. It runs a long time on a charge and it has apps that respond quickly for movies, reading, browsing, mapping, and note taking (all things I do while traveling).
The Surface Pro is where I do development (generally in WSL2 these days) once I've arrived somewhere that there is free WiFi and access to AC power. I will typically use it with a USB device or two as well (such as flash drives, wireless connections, and embedded development boards) Its ability to drive a couple of 2K screens and give me a "full up" developer experience is appreciated.
I sketch more on my iPad even though I like the drawing "feel" of the Surface Pro better. The SP feels "clunky" when I try to use it in tablet mode.
When I use them together its generally the iPad for reference materials and background music while I'm writing code on the SP.