for glute use a 22 or 23g 1-1.5" needle
for quads, delts, biceps, triceps, pecs, traps, calves, basically everywhere else, use a 25g 1" needle
always use an 18 or 20g needle to draw out your gear from the multi use vials, then change to the size you plan on using for your injection. this way you have a nice fresh tip to peirce the skin with so it goes through easier. the rubber stoppers will slightly dull the needle end and make it a little harder to push through and will cause the buildup of scar tissue a little faster which will make it a little harder to push needles through the skin