Which Wizard specialty is best?

[Klorox]

I'm most interested in not missing out on some good spells, more than the bonus spells you actually get.

I remember in the Baldur's Gate games liking Conjurors the best, because they only missed out on Divination spells, but now they miss out on Evocation spells, and I'm a bit more hesitant to go that way.

This character will take at least 20 levels of some Wizard class, and will be working in the same party as a Sorcerer.

TIA

[Jelaweb]

I favour Diviners (opposite school Conjuration). I rarely conjure monsters and let other spellcasters do all the acid magic and the odd spell Conjuration spell that I might actually use.
If you like your Summon Monster spells though, this is not the correct school for you. As such, it depends entirely what the character does. Most of my wizards use defensive magic (let the sorcerers do the blasting), with the odd attacking spell for good measure. In this respect Diviners are ideal for my purposes.

[Klorox]

Hmmm, I'm defintely looking for a support caster behind my nuking sorcerer here.

[Jelaweb]

Well, you have to choose what spells you want - you don't need that many. Just write a short list down and get all the schools for them. By a process of elimination, you can narrow down the wizard school you want.

Say you really want Grease, Web, Fireball, Vitriolic Sphere, Chaos, Shades and Finger of Death as your base set of spells.
There is no school that allows all these spells.

1) Narrow down the school choices:
You would not a Diviner or Evoker, because the "majority" of spells (3 out of 7) are Conjuration - so you can immediately cross these schools off the list. All the others have just 1 spell, so you must sacrifice at least one of those spells...
2) Decide which schools you really want to keep:
If you really want to cast Evocation and Necromancy spells, you can cross Conjurer, Enchanter Illusionist and Transmuter and from your list...

So far, we are down to a choice of Abjurer or Necromancer to pick.

3) Sacrifice spells:
Sacrifice Shades (and all Illusion) and all Transmutation = Abjurer
Sacrifice Shades (and all Illusion) and Chaos (and all Enchantment) = Necromancer

Although this is a simple example, the idea is sound. It also means that when you do choose your wizard school, it will be interesting to play, because you will suddenly find you cannot scribe certain spells you might want. It will at least make the game more interesting.