Druids are a priest class. Calling upon nature they can heal but they also have powerful damage spells like fire and lightning. Because of their healing, damage and evacuation abilities, druids are always welcomed in groups, but through the use of kiting, many prefer soloing. Enchanter spells focus on manipulation of the mind, and this mental acuteness gives them more spells than any other class. With spells like Clarity and Charms it's no wonder that Enchanters are sought after by groups all over Norrath.
Mages work well in groups but can also solo with one of their pets.
Monks are the masters of body and mind and use these tactics to defeat their enemies. Because of this they have the ability to deal out great amounts of damage without the aid of weapons or heavy armor. Monks make terrific group members and are often sought after as pullers. Necromancers are the masters of the dead, reaching beyond the bounds of the grave to magically manipulate their dark minions. With the ability to command an undead being the Necromancer makes an impressive group member but they can also solo most effectively.