Liosliath
I am by no means a super master expert at these games, but here's what I did in Wiz 6:
Mook Fighter > Ninja > Lord
Human Fighter > Ninja > Monk
Hafling Fighter > Ninja > Samurai
Human (Female) Priest > Lord > Valkyrie
Elf Mage > Priest > Mage > Priest > Bishop
Rawulf (Female) Bard > Samurai > Mage > Bard
The goal was to take this party through all three games. Three fighters level fast in the beginning, use good weapons, and have good HP. I rolled them all to start with enough stats to change to Ninjas at any time. It was REALLY painful to get the Mook to a Lord because the default Mook personality is like 6 or 7, so I had to save scum every level up to ensure I got up to 12 personality within a reasonable time. I don't recommend trying this for a first time run. The monk and Mook were made to take advantage of long reach weapons in Wiz 8, the Samurai was made to take advantage of the Muramasa sword in Wiz 6 and 7.
The priest was a backup healer, female so she could be a Valkyrie and poke with spears from the back row. The mage is a nuker/backup healer, I class changed him back and forth between mage and priest to max his casting skills and farm spell picks. The Bard ended up as support/backup nuking. I class changed her to get her extra spell picks and skullduggery (lockpicking). She's female because there are good stamina restoring accessories which are female only in Wiz 8.
In Wiz 7, I had to rotate the front rank through another round of ninja - samurai to farm skill points and max out their ninjutsu and kirijutsu. The valkyrie, bishop, and bard I just did the same class changes over again for spells and skill points.
In Wiz 8, I learned that when you auto-import characters it assigns the bonus points for you, in very annoying ways. I like melee characters to have Str & Dex maxed which only Fighters get when they import, so I class changed the Lord, Monk, and Valkryie into fighters before import. The Mook stayed as a fighter to use Blade of Giants, the other two reverted back to their classes of Monk and Valkryie right after importing. The Samurai I converted to Ranger before import since I was going to stick him in the back row. The Bishop and Bard I left alone.
This party was intended to avoid all RPCs in Wiz 8 and use all extended reach weapons. Extra RPCs make this party easier and you can use whichever weapons you like.