A Conjurer would make a better choice than the Necromancer, if you are looking for power. Personally though, I always choose Necromancer, not because I think it is more powerful, but because it is more me( you know... roleplay and stuff?
).
There are 14 spells belonging to the school of Illusion, and 11 spells belonging to the school of Divination. So actually... there are more Illusion spells than Divination ones.
A Conjurer mainly loses out on 3 spells only, True Sight, Identify and Wizard Eye.
A Necromancer loses out on the following, Mirror Image, Project Image, Mislead, Spook and maybe, Simulacrum.
Mirror Image: It makes your Stoneskin last longer and also takes the hits for you from spells and area of effect spells.
Spook: Ever scared a Dragon before?
This spell eventually gets potent because the target has a -6 penalty to its' saving throw.
Mislead: Undispellable invisibility... yummy... if a bit cheesy.
Project Image:
Eyah!
This has to be one of the cheesiest spell a Mage/Sorcerer can have. This spell basically means that your Mage has an additional round of spells minus one.
Simulacrum: Not as powerful as Project Image, but still, it means extra spells if you want it. I do not use it, but others do.
Anyway, if you want to talk about soloing, a Conjurer will have an easier time than the Necromancer. If you have a party though, then the Necromancer is a very viable choice. I played as a Necromancer when I had an Evil party. Heh, heh... petrifying the wildlife was fun.
Conjurers were the number one choice for soloing at the BlackIsle Forums if you wanted to solo a Specialist Mage. Necromancers were second.
Just to let you know.