APFS or Mac OS Extended for a thumb drive?

Does not matter much but I use APFS because new macOS defaults to it (a bootable USB macOS installer still needs Mac OS Extended for the Terminal command, though).

Mac OS Extended (GUID) if I have to use the drive in a High Sierra or earlier Mac that does not support APFS (High Sierra does).

FAT (MBR) for a smart TV and small files to Windows.

exFAT (MBR) for larger files to Windows (somehow GUID displayed only a small space on a 128 GB USB drive on Win 10).

If you want to put a Photos Library onto the stick, it could be either Mac OS Extended (Journaled) or APFS, but not case-sensitive, or you might have problems with videos.