So my question is: Do you not want to die as quickly, or do you want to try and kill them faster than they kill you? If you answered yes to the former, then you want to be a tank (or a tanky-damage champion like Garen). If not, then we need to dive a little bit deeper...
Do you like to carry games later on, pulling your teammates on your back for the final push? Or do you want to eradicate your enemies quickly, and a bit early in the game? If you answered yes to the former, then you want to be an ADC. If not, then we need to dive a little bit deeper...
Do you like using skillshots, and the beauty of a precise attack? Or do you want to target one particular enemy and have him destroyed by the push of a button? If you answered yes to the former, then you want to be a Mage. If not, then we need to dive a bit deeper...
Do you like to be hated by all your friends and family, get everyone in the game, even your teammates to rage on you? Or do you like friendships and sunshine, sprinkled with happiness? If you answered yes to the former, then you want to be an Assassin. If not, then we need to get out of the water...
AND DON't PLAY LEAGUE OF LEGENDS!
The End.