I'm offering a balanced, expert party of: Fighter, Rogue, Valkyrie, Ranger, and two Bishops (one Divinity/Wizardry, which gets all buffs, and the other, Alchemy/Psionics, which makes money for the party, and messes with enemies' minds).
The melee is handled by the Fighter, Berserking with dual weapons up front, the Rogue, Backstabbing with Dual Weapons up front, and the Valkyrie and Ranger on the flanks, hitting from extended range with their Polearms. The Bishops' melee isn't important until later, until they can get Staves of Doom, hitting from extended range.
The range is handled by the Fighter, Rogue, Valkyrie, and Ranger (ranged crits), using bows and crossbows. The Bishops' ranged attacks with slings isn't going to be a factor until way later in the game.
The magic is handled by the two Bishops, getting their spellbook and realm skills good in the Monastery, before Arnika, when I have to worry about friendlys "helping" me in battle. This could be supplemented with the Valkyries and Rangers magic, but they are more suited to melee and ranged attacks, and will worry about their magic later (no Powercast).