i learned on a 1981 kawasaki 440, so my vote is for any 80s ujm. i know it's not in the holy trinity, but since you WILL drop your first bike (and most likely your second, third, fourth, etc), you should be on something not worth repairing. i'd be happy to provide a review of the bike, along with how i almost rode it off a cliff, slid through numerous red lights, and learned to push-start it since the starter was fried. nothing will teach you to appreciate modern bikes like experiencing the old ones...