It all depends. If your gear is in E.O. then as small as 27g. If all oil then around 21g. then as to where you inj. should determine the length.
glutes 1.5
delts 1
quads 1
i never used a large gauge to draw so as to not damage to stopper too much.
and as for brand that would be B.D. I've had teramu or what ever their called seem like they had a barb on the end.