I use 29g half for everything.
I’ve used 31g but it takes absolutely forever to pin even a water based injectable, forget about oil.
29g is painless for subq and IM. I pin everywhere with that size, even with glutes. Im mostly lean enough, but just to make sure I’m getting it deep I don’t just put the needle in, I bury it deep by pressing it in so that it indents into my glutes.
25g one inch isn’t bad at all I just like 29 better.
23g is okay but I start to notice a little pain, that’s the biggest I would ever go.
I have 18g with 10ml syringes for backloading a lot of 29g at once, but the 18g is bigger than some of my piercings, I would be horrified to pin that.