I’m self taught, and I tend to think of flats because I tend to downtune. I think others choose the flat or sharp based on their desired key. That doesn’t help me describing a tuning if I’m playing out of the tuning’s assumed key! I have adopted one set of tunings which requires bringing the second string higher than the first, which I usually dedicate to a guitar with the strings swapped so I don’t break them all the time. (Adapted from very closely watching performances by Kelli Rudick if you’re curious.) I always describe the 2nd string tuning with sharps unless I have a good reason not to.

None of this is meant as advice, it’s just how I reason about using the instrument myself in ways it wasn’t necessarily intended.