I use 25G 1 inch for every site, side delts, rear delts, lats and sometimes i add pecs in rotation.
I've no problem with thin needles but i strongly believe on going deep with IM. I'm pretty sure many dudes that use half inch insulin pins for IM rotation, they're just doing shallow IM/subc and fool themselves. Even at 7-8% bodyfat with enough muscle mass a half inch may be good for delts but even pecs or lats i wouldn't be comfortable doing them with short needles, it's funny some guys doing glutes and ventroglutes with slins and think they're reaching muscle when they're +10% bodyfat.
Also, i believe that scar tissue of unfrequent shots with a 25G versus a scar tissue of a 29G and daily shots would be pretty similar. Piercing the muscle with a somewhat thicker needle 2-3 times a week vs piercing the muscle with a thinner needle everyday is close IMO.
So i don't agree at all with those who end up doing every day shots just to avoid a thicker needle in order to not create scar tissue. If you want to avoid scar tissue you can do subc and call it a day.
The perfect scenario for me is doing 3 IM shots a week with a thin needle like 27G or 29G and 1 inch long. Unfortunately i can't find anywhere here in my country a gauge like this so i'm doing 25G. I wouldn't mind wait another 10 seconds for the oil to come out.