site injections redgarding Needle size. Help ASAP!

[Xtreme2001]

I'm going in abut 20min to pick up some needles.

I'm going to be doing Site injections in the biceps. I need to know what's the Best size for it? Smaller or Larger? If I remember correctly.. was the best size 25g? 5/8inch.
Would 23-21 be better or worse?

 

[Terry]

less pain with 25ga

 

[Xtreme2001]

Thanks guys.