I always considered stealthing to be a per character check, because I have a hard time imagining a paladin in shiny, heavy and loud armor stealthing silently, just because a rouge with stealth expertise goes next to him.
I was under the impression that my approach was according to the rules, because PHB 175 states that “the DM might ask for a group ability check” and furthermore “[group ability checks] most useful when all the characters succeed or fail as a group”. This doesn’t have to be the case for stealth imho, where it is very well possible for one character to fail and be spotted, while the others are still hidden. It can even be useful, if just one character is spotted the guard may be like “You got lost or something?”, however if a whole group appears they might immediately ring the alarm. Of course it can also be annoying to barely be able to stealth while wearing heavy armor, but taking it off is an option.
However in this comment nick012000 states that technically this should be a group stealth check. So I got curious if I was missing something. Maybe a different rule in a different book, or something else that requires or recommends stealth checks to be group checks.
Note: I do use group checks, for perception, or if multiple characters investigate something etc. Just not for stealthing.