They are an allround class.
Holy Paladins are healers. They are very good in 2on2 arena teams with a Deathknight for example. They all focus on healing the other member wich will destroy the team.
In PVE they are one of the best single target healers.
Ret paladins are High dps dealers. They are good In battleground but not taken very often in Arenas.
Protection paladins are not a pvp class, they cant really kill anyone in PVP. They are the PVE tanks, and are very good at it.
All in all Paladin is a very good PVE class and a good PVP class, especially Holy pala.
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