They are offering the Gift of the Valar in the store for a short time which instantly advances a character to level 50.

Which class would be the best use of this item? By that I mean which class would be easiest to power level other classes? Which classes were just too tedious or slow to level that getting one to 50 instantly would make the class more playable? Which classes change in style after 50 that make the classes more enjoyable?