Post by cranial
Uh, he's talking about lich king, not the current live wow.
In LK they both will be tenacity pets, aka, they will both be able to tank, and assuming that both of them will have the same talent builds, the difference comes down to their special skills.
First lets look at crocs, they get Bad attitude
http://petopia.brashendeavors.net/wotlk/skills/skills_badattitude.phpIt is pretty cool, and lasts an impressive 45 seconds, but on the flip-side, its got a horrid 3 min CD.
So unless, you plan to multi-mob tank with your pet once (or twice, depending on the fight length) every 3 minutes, crocolisks arent a good tank-pet choice.
Now, lets look at Bears, they get Swipe
http://petopia.brashendeavors.net/wotlk/skills/skills_swipe.phpThis thing hits 3 mobs, and has a 10 sec CD. So, multi mob tanking with a Bear will be faster than with a Crocolisk.
For now this info pertains to only the beta in its current version at the moment.
So, further changes might be expected. However, in current state, bears seem to be the best multi mob threat handler pet.