Well seems like everyone said already. Most of tanks skills are from GLD (Provoke,convalescence,Awareness). From MRD (Foresight,Bloodbath,Mercy Stroke). PLD is an easiest tank to play and has similar play style to DRK and you don't have to worry much about defense if your gear are up to date with dungeon level. WAR is more active tank than PLD and requires a bit of tp management. It's all depends on which one you want to play an iron wall tank, or a massive HP and quick dps tank. As what most people said just get tank cross class abilities first then decide which tank you want to play.