Leveling a paladin in World of Warcraft can be very hard. Even at the higher levels. My friend Mathew started out leveling his paladin very slow. When he reached level 40, he was going extremely fast instead. That's the advantage of a paladin build for Area Of Effect grinding (AoE). Paladins and frost mages are the only classes in wow which can do this effectively.
He was recently kicked out of his guild. I asked him what the reason was and he said to me: "I leveled to fast and the guild members falsely accused me of using bots to level." I smiled and asked him: 'Well, how do you level your paladin so fast then?'
When leveling a paladin, an Area Of Effect build is the way to go. You level slowly at lower levels, since your initial damage is not very high. When you progress trough quest and become level 40, matters will start to change. You will then have the attack power to grind large mobs. A frostmage doesn't have as good defense as a paladin, they die easier. That's why paladins rock when it comes to grinding.
You will have the core talents of you Area Of Effect build and you can start grinding large mobs. These main talents are Blessing of Sanctuary, Reckoning, and Holy Shield. In addition, I also got a spiked shield and other gear that increases defense ratings.
If your defense is high, you will out-speed a frost mage very easy in terms of leveling. Frost mages have a very low defense and have a higher chance.