Actually, the bear attacks slower than other pets, on account of its Brutal Mauling skill (which, as far as I can tell, is just a normal attack with extra flavor).

To complete what everybody said: indeed there is no "best" pet (there is just a "worst" pet - bears). The assumption that spiders are the best pet is just wrong. They all have an attack speed of 2.14 sec, except bears with Brutal Mauling (2.61 sec, and it doesnt deal extra damage). All the pets have a base armor of 80, deal 17-41 damage, and have 480 health (for elder lvl 20 pets).

I would just add that the Bear can be a superior pet for spell casters (if you are crazy enough to be a spell caster with a pet - like me with my monk). The reason is that AI enemies will interrupt the bear instead of you.

Pets DO have different types of damage: Blunt, Piercing, Slashing, etc... Spiders have piercing I believe. I think spiders got the hype because it was so easy to get a Dire or Elder one without training.

But we all know the trick to get a dire pet within 2 hours! Or is it just some of us :P

GW wiki pet guide
http://gw.gamewikis.org/wiki/Animal_companion
(some informative links at the bottom of the page)