Haer'Dalis is far better than Cernd. If I want a druid, I choose Jaheira, fighter/druids are so much better than straigt single classed druids and Shapeshofters are the worst kit in the game, imho.
I always have Haer'Dalis in my party, him and Aerie make a great team and even have a mini romance (while I try to imagine that he is romancing my character instead...), he can pickpocket and cast spells, his only weakness is his low constitution, but take one of those potions of fortitude before a major battle and he is a great tank. I have found Haer'Dalis highly effective against Kangaxx, his abilities to cast spells and fight means that I can actually put Haer'Dalis and Aerie two on one against Kangaxx, no problems.
Cernd's werewolf form isn't that great, he can still be easily killed regardless. Sure he has 18 wisdom but then he dies in a battle, due to his weak stats, then you have to have his spells memorised all over again. I had to give him potions of fortitude, agility and all sorts of others before certain battles. In the end I just chucked him out after his little quest.