Chest/shoulders. Ive got some moderate scoliosis so my lat is like 5% bigger on the right, and chest is like 5% bigger on the left. Makes benching weird cause going straight up and down isn't natural. Chest itself isn't too bad but any chest exercises stresses my left shoulder because I have to compensate.
chest, apparently it doesnt want to progress at the same rate that everything else does, even if im doing it balanced. I always feel weak on my chest, ridiculously strong on triceps and normal on legs. Not having problems with my back in years, in fact, i corrected a small deviation i had to the left few years ago just by stregthening it
Abs by far. My diet isn't great (damn sweet tooth!) and I never see results, so it tends to get half-assed or skipped. Legs are kind of meh, bad knee doesn't help. I used to dislike chest, but I have gotten much better at it. If I could, I'd do arms all day / every day.