Samurai: If you like high DPS (Damage per second), but not so heavy armor. Samurai has low HP and bad armor compared to the other warrior specs. Their skills are great for 1v1 pvp, but not good for fighting outnumbered. Really good PvE class.
Dreadknight: If you like high HP, great armor and good skills. DK got low damage, but can use full iron and diamond helmet/boots. The DK HP is the second highest of all classes and DK do well surviving big pvp battles considering their armor and HP. The skills is mostly offensive.
Paladin: Defensive class, low damage and high HP. Paladins has the highest amount of HP of all classes and the best armor (Full iron, diamond chest and leg). They have only one offensive skill (Soulfire), the rest is healing and defensive skills. Good for tanking, but bad for mindless slaughter.
Dragoon: Mobility and damage. Dragoons got very good mobility with the skill jump and their damage is decent. Their armor was nerfed a bit on Dragongarde (Chain helm/boot, iron chest, diamond legging). Great deal of HP. They have many good skills that matches their mobility.
I'm a Samurai, good DPS is my thing.