I believe best length is 1" for quads. I almost always shoot with a 25 gauge, and syringes/needles are so cheap, I'll usually draw with a 23 g and replace the needle and shoot with a 25 g (oil) or 27 g (water).
I have heard that if you are using multi-dose vial, and you draw with something thicker such as 21 g or 19 g, it could cause small pieces of rubber to enter your vial or compromise the sterile solution?