Which one is more fun/more rewarding to level?
I have always loved Shadow Priests and Warriors.
I don’t mind healing or tanking (especially since I have found out you can 2 hand tank for a while).
I have narrowed it down to either a Gnome or Orc warrior and either a dwarf or troll priest.
Leveling for me is going to be slow as it is with the amount of free time I have. I just want to find out which ones easier to level and most rewarding at the end.
go warrior, help the tank shortage 
we have enough healers
We have more than enough warriors, they just need to man/women up and tank. Not like you need to be tank spec or even use a shield until dual spec is available anyways. In fact it’s optimal to 2hand for threat.
There’s not much point in using dual spec for a tank-specific spec for warriors anyway, even if they want to tank dungeons.
Priests are pretty solid healers.
Warriors are the best tank and the best dps in the game.
So it depends on what you want to do.