25 gauge 1 inch for glutes. For all other body parts (chest, delts, upper quads) I use a 29 gauge insulin pin. I draw out the oil with an 18 gauge needle and then store it in a sealed baggie for future shots.
Normally pin with 27G insulin 0.5", tried 29G the other day and surprisingly it was possible to draw my test (after warming it up). Very painless injection and minimal scar tissue with the smaller gauges.