This is a general guide (While it is up to you, I've played over 70+ characters I think I know where I belong) to what classes are best suited for what.

Clerics: The Steroids and doctors of any expedition, while depending on the build, this class is always invaluable to any expedition, be it healing members with there wands, or slamming the enemy with Divine blessings and turning, Clerics are always a must to any expedition. There ability against undead is also phenomenal and any expedition against undead should have a cleric.

Bards: The true adventurers, the inspiration, mechanically speaking, among the strongest classes out there, Providing the party with the lore mastering abilities and bard song, ability to use practically any device, and cast limited magic, this Class is suited to all lines of a party, and always a must to have along.

Fighters: The discipline of a group, these warriors are often intelligent, brave, and resourceful. They are meant to fight, though they often rely on clerics and wizards, or other spell casting classes, They are there to hold the front line, and see the party through to victory.

Barbarians: the Raging tempest of a Party, these warriors are meant to hew down enemies without mercy or discipline, incredibly hardy, these warriors can take immense amounts of damage, and dealing incredible damage to the enemy so weaker classes can come in and mop up there mess.

Wizards: The tacticians of a group, this class is best left to making there own position in the party, usually in the back. But a mage prepared for combat is an immense foe, or ally, and can save the day in one or two spells.

Sorceror: While Limited in spells, they make up for it in sheer casting strength, these special people are useful if you know what you up against, and not always reliable, but if your looking for a long drawn out campaign, a sorcerer is always better than a wizard in such a circumstance. Always in the rear.

Rogues: The sneak of the group, dealing with locks, traps, and other suspicious things. When assaulting forts or moving across enemy lands, a rogue should always be by your side dealing with traps and pits. While stereotyped as greedy, an honest rogue is the best friend you can ever have. Position in group up to them.

Rangers: These wildsmen are reliable, and against there chosen foe, fountains of hatred and destruction. They are your scouts and guides in the underdark, and there opinion should always be respected. There abilities in combat and stealth make them a balanced class, suitable for any occupation. Position in group should be left up to them.

Druids: Your powers of the wilderness, the best of friends, your wisdom in despair. Druids can cast spells that can increase the protections of warriors, and there polymorphing and taming abilities are always useful. But be warned, necromancers and abberations sympathizers, the fury of nature comes upon you should they find you. There position in a group should be left up to them. There companions are also mighty warriors, can should always be respected.

Paladins: The shining light in the Underdark, these Divine Warriors are the best people, there abilities against undead are magnificant, there holy blessings destructive against all undead. fearless, reliable, and honest, paladins are powerful allies, and even worst foes. Always at the forefront of a fight, leading the group to victory in the glory of there god.

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While this is just a brief outline of the parties, I truly think it covers all aspects of the class. While the wizard, bard, and cleric classes could be discussed on all builds, I truly believe that these classes are what they are, powerful when built right, even more powerful when used right. I've seen wizards decimate entire parties, fighters that took out a group of wizards, bards that hewed down 7 opponents by themselves before being defeated, Clerics that soloed entire quests. Paladins that, well, you get the idea.