I tend to leave it exactly as-is. In the summer if I'm noticing a particular amount of sweat or scent, I'll trim it down to a more manageable level, but otherwise I just leave it alone.
I hate underarm hair, visible underarm hair specifically. Shit's nasty everyone has shitty deodorant clumps because they use shitty deodorant and it bothers me so I strove to never bring such a blight on humanity myself.
I leave mine as-is but have been thinking about trimming as it does get warm under there now the sun's coming back out, it's pretty thick. Smell isn't an issue as I wash and use deodorant but I get sick and tired of the damp patches in the Summer. Interested if trimming would have any affect.
Electric trimmer buzzed down to the skin. Takes like 30 seconds and I do it every month or so. Armpit hair stinks and is uncomfortable in any sort of heat or humidity. I can't think of any upside to not clipping it down.
Leave it, nothing worse than armpit stubble after a day or two. Also the way sweat just rolls down my body when there's no hair is gross. I'm not especially hairy so it isn't really a problem anyway