What is the best type of character on World of Warcraft

That depends on what racial spells you want, and what class you want.

mages and warlocks cast spells of all sorts that are powerfull but can only wear cloth

druids have nature spells healing and daggers they can also wear leather, they turn into different animals:
Bear- a tanking form where you can take in alot of damage but you cant deal a lot of damage.
cat- A high damaging form that does not use spells but claws and bleed effects
Tree- an only healing form
Moonkin- a spell damaging form that focuses on combining different spells to make a lot of damage.
Cheetah- just a way to get around faster than walking
Flying form- you turn into a bird and fly, does not damage
Swift flying form- a faster bird only available after getting artisan riding

Warriors take in a lot of damage and are usually tanks though some do alot of damage, bear form is very close to a warrior

Paladins can heal, take in damage, and deal out close damage.

Shamans can heal, damage by spells and damage by close range.

Priests can heal and deal spell damage.

Rogues are only close damaging class and they do only single target, cat form is very closely associated with this

Hunters do far away damage but not from spells but bows and guns, they have a pet you can tame of your choice but some are not tameable, only through a special ability

Death Knights can damage close and tank, but you can only get them after you get a character after level 55 because they start off at level 55