What class is the most fun for you to play (a small example of what makes it fun would be nice)
This goes more to people who actually play more than one toon as those who play only a single one tend to have a more biased opinion.
For me
1.- Frost Mage.- lots of control freeze + ice lance combos
2.- Frost DK.- Lot's of AoE, great Cooldowns excelent survivability (howling blast & army of the dead)