[Radek]

For SoA only, I recomend dual class:
1. ranger/CLERIC, dual immediately, blunt weapons, sling, 2 weapons
2. kensai/MAGE, dual at level 9, staves, axes, 2H weapon
3. swashbuckler/FIGHTER, swords, katanas, 2 weapons, short bow, spend all your skill points with Disarm Traps (100) and Detect Traps (100) and give the rest to Pickpocket. Dual immediately.
Install level 50 rules because this party of three will reach level 28 or so.
I have no experience with ToB. As far as I know, multiclass characters are reported to be more advantageous than dual class ones. A serious analysis would be highly appreciated, for example, what is better? High level of a single/dual class character or versatility of a multiclass? At least one thought: you will never need a super level thief unless you are about to specialize in backstabbing or, of course, if you want to play a thief. Potions of Mater Thievery will help you when needed. Therefore, a character with a thief part would be dual class in ToB, too. Perhaps, the character would dual later than in SoA.