Nord Elite Skill Wolf/Leopard
I play an engineer and havent gained enough skill points to try to any other one apart from the bear.
I really liked the bear, the knockbacks are awesome and its pretty tough, however i found myself going back to my class based skills (engie supply drop at the moment) as it just didnt appear to have as much of an impact as i would of expected, definatly enjoyed it though, and would be interested to know if they are based on the stats you currently have in any way.
For general PvE exploration, I prefer the Snow Leopard transformation above anything else (even Elementalist class elites), due to the Stealth. By using it at appropriate times, you can sneak past a large number of mobs to reach that difficult to get to point of interest or skill point.
Wolf is the best CC, due to having both a fear and a knockdown to provide interrupts.
Also note that Bear will increase your health and durability.