If you take 'less powerful' decision for roleplaying reasons, that doesn't make it less optimal, you have merely decided to optimise for fun, rather than for greatest power.
I'm playing in a game now wherein I'm running a Clr3/Wiz3/Mystic Theurge 5, and I was originally aiming for archmage (as arcane reach, mastery of counterspelling, mastery of shaping, and spell power high arcana do
not specify arcane spells or arcane caster levels (as appropriate), as the other archmage high arcana (arcanum?) do), but that 4th level of loremaster grants a bonus language, which because it states, "A lore master can learn any new language [like you'd want to learn one you already knew? WTF?]," means my character could pick up Druidic.
Druids are a major force in the campaign and being able to speak and read their language would be an incredible coup for a non-druid.
So I'm still deciding between loremaster and archmage, assuming we get to that kind of level.
Why'd I choose mystic theurge, a class everyone knows blows? Because I knew I could crush the campaign as a single-class cleric, druid, or wizard, and I didn't want to because I like the DM. So I hobbled myself to avoid temptation.
Why go loremaster instead of archmage? To piss off the campaign world. Because that's fun.
It's a lot easier to aim for fun when you trust the DM and the DM trusts you.
Ramble. Ramble.