I am new in the game and I can't choose what to be my main character! I stop choosing on Paladin,Hunter or Mage. What is the fastest lvler and who is the coolest.

Personally I'm in love with Mages.  Mages and Hunters level very quickly.  Paladins I'm not to sure never understood them or liked them lol.

I currently have a 39 Ret Paladin. It was my first toon when i started playing wow and since i have started i have also got my feet wet with some of the other class's I would have to agree on Mage's being really fun to lvl and very powerful. It really depends what you area looking for: If you want to do lost of dps (damage per second) then i would go with Hunter and then Mage. If you want to control big crowds and to do great dps at same time the go with a Mage. If you want to do Some magic and healing and dps then i would go with the paladin. I hope this helps out a little, it truly depends on what spec/talent you decided to do with each toon depending on what kind of character you want to have. As far as DPS/Healer/Tank. So i would say look at the spec/talent tree of each one and see what you would be intrested in.

Mage

Mage all the way. i like BE mages for the enchanting bonus and the extra mana and they look cool

hunters r ez 2 lvl but if u n pvp(player vs player) then u wont do so good. i think pallies r fun 2 play kinda ez 2 lvl and good n pvp.

hunters PWN in pvp

I personally like my mage(level 70), but my pally is fun too(level 25, still leveling that alt) i like those two, becauses they have some difficulty in play style. Mage has some challenge, which makes them fun, i have fun with pushing the limit, pally has 3 or more safety nets, but i can take on like 5 things, which pushes the limits imo(redoubt helps a ton)

Paladin

I would say hunters due to the fact that they can solo and they were made to destory clothies and also they have sick dps, i normaly play my 70 mage but my friend let me play his 68 hunter and holy crap that crap inspired me to make a 70 hunter :D