Here is a list of the skills for the Paladin.
Level 0 - Holy Word : A wave of soothing light seeks out and heals your most injured ally (30 sec cooldown)
Level 5 - Wrath : Imbues your sword with holy lightning for 10 seconds, which chains to nearby foes (30 sec cooldown)
- Aura of Light : Converts all damage taken into healing instead for 10 seconds (40 sec cooldown)
Level 10 - Stalwart : Increase the paladin's armor by 15% (Passive)
- Swift Justice : Both movements and attack speed are increased by 10% (Passive)
Level 15 - Divine Intervention : Redirects all damage from the group to the paladin for 10 seconds (30 sec cooldown)
- Radiance : A blast of divine fury knocks all the enemies to the ground while healing the party (30 sec cooldown)
Level 20 - Bastion : Increase the paladin's maximum health by 20% (Passive)
- Power of the Word : The power of your healing abilities is increased by 20% (Passive)
Level 25 - Sentinel : The paladin now grants 25% of their own armor value to all of their allies (Passive)
Level 30 - Word of Asylum : Your Holy Word ability also leaves a lingering shield, nullifying damage for 5 seconds (Passive)
- Word of Retribution : Holy Word now strengthens its target, boosting their power by 50% for 10 seconds (Passive)
I have found that the most efficient skill set for arena fighting is the following : Holy Word - Aura of Light - Stalwart - Radiance - Bastion - Sentinel - Word of Asylum.
If you need a guide for any other character, feel free to leave me a comment