If i had a 100% guarantee that i could become any class i wanted, and NOT die ( or at leas get ressed ) id become a warlock or deathknight.
As for a single spell, hard to chose. I dont want some silly cure disease, if i could have any spell i wanted id want it to be something i could benefit off of.
Mind control would be nice to take control of the world and feed the perv in me, but diminishing returns will eventually make em immune, and anyone who watches the movies know that when one person becomes immune, he kills you and frees the rest.
The shaman self res would be nice, but its only once every so often, and where the hell am i gona find a shaman ankh on earth?
Soul stones would be nice, but with out drain soul how am i gona make em?
So, ive come to the conclusion that i would learn a spell that lets me learn every spell that the class i chose to become knows.
"And the earth will stand still the day i release my army of Demons and fire upon the nations leaders and citizens, none will be freed from my tyranny, none will resist my will, and none can hide from the destruction that will ensue."