Size the syringe to your application to limit the amount of draw/fills for a given recipe.
Use a 1ml and 3ml luer syringes with 20g blunt needle for best control of thin material addition such as concentrated flavorings or pure PG.
Use 3ml, 5ml, 10ml, 20ml luer syringes for PG, VG and Nic base liquid transfer. 14g for VG or quick transfers, 16g and 18g for PG/VG mixes.