I rarely take highest efficiency into consideration. For example, I got 99 Slayer without ever using a cannon, 99 Woodcutting with yews (note: pre-ivy), 99 Agility at advanced gnome, and prefer abyss Runecrafting as opposed to using graahks. That's all I can remember off of the top of my head. I'm sure there's more. Most of the most efficient methods aren't very fun to me, and if I'm not having fun, I have no motivation to play.