|Alliance of Light||Union of Fury|
Classes are considered to either be strong in a Party or played Solo. For example, a Defender/Guardian has very high defense, but low attack, and a Pagan/Mage has low defense but high attack. If these two classes party, they can use their strengths to have both high defense and high attack to defeat their opponents. Solo classes generally have more balaced defense and attack and do not depend so much on being in a party. This does not mean they cannot or should not party, only that they would not significantly benefit either way.
If you read the initial stats for each class you will see there's a slight difference in each faction's counterparts. This happens because each race gets a slight bonus on creation. (See Race Bonus on race)