Conjuration is usually seen as the best school because it does everything. It has good battlefield control spells, spells that target different defenses, spells that bypass SR, and summoning spells, which are among the best in the game. Conjuration even has good blasting spells. Snowball in particular is the best first level blasting spell.
Yeah, Conjuration (Teleportation) is really difficult to beat.
Divination (Foresight) gives you a ton of free rerolls which can be vital as well.
What kind of campaign are you playing in?
Spell wise I'm always loving transmutation, but as far as class abilities it's not so great.
My vote goes to Divination. Let me explain in depth:
You're a wizard, and you go first.
Wizards always get the nicest toys depending on what you want, and a Divination wizard uses them before all the other kids.
Luna Nova Academy
Divination is amazing if you are ever making attack rolls (prescience), need to pierce spell resistance, or know a save is coming... so, almost always.
The problem with divination is having to choose a divination spell as one of your two free spells a level. This sucks pretty harsh at low levels.
Low levels also have fairly situational divination spells to put into your school slots.
