I would just get 28 until you get the hang of it. 28 is a bit thinner, but gives more resistance so you don't have to worry as much about needing a ton of wraps. Even though I have been building coils for a while, I still use 28g from time to time. It is just a good all around wire. If you are dead set on the 24 or 26, I would tell you to get the 26.