Conjuration, uses willpower. A very popular magic school.
Invisible servant -> social spell (out of combat) that gives you a one hour duration "animating force" that can do anything not requiring a skill roll. Has 1s in all stats if it matters. Well that gives it a speed of 2 and a run of 12 for carrying that bag of grenades (it lasts an hour, you just have to cast it out of combat) over to an enemy. Or a friend if you're a practical joker who worships Malal. It can't drive... no it can, it's just terrible at it. I recall that the book 2 vehicle rules cover non-skilled driving and it just defaults to the worse of dexterity or intelligence.
Blink -> the absolute favourite level 1 spell of non-vamps and non-were. Combo-Ok somatic 40m line of sight teleport for the low cost of a DC 15 casting check. 4k3 is plenty to cast it almost all the time (~15% fail rate and 93% of the time you do get warp rolls for being unsanctioned you still won't get off the first table... well my first table, there's a 30% change by the book's table).
Web -> Combo-Ok VSM puts a 5m radius of webs centred on a point within 25m and all in it are immobilized for your level in rounds. As written there's no save, no escape, and no size limits. Although nothing prevents forced movement out of it. Also nothing about what happens if you drop it in mid-air or on water. Needs work.
Lesser Servant -> full round summons to get a small creature or entity to aid you. All stats and skills at 2 and lasts a minute per caster level. No pilot? "I summon the spirit of Bob the pilot!", 4k2. No arcanist? Summon something, 4k2. Lock needs to be picked? Summon something, 4k2. Got a pile of laz guns and an oncoming horde? Spam gene-geneered combat monkeys to fight for you. I'd consider it a level 2 critter for ballistics and weaponry, heck even size 2 to keep things simple.
Call item -> interesting spell, social so no casting it during combat but when cast on an item that you can hold in one hand you get to summon that item to your hand as a free action. No distance, not expended, limit one such enchanted item at a time. Nice if you want a cheap artifact weapon, get a knife (vary common, artifact 1) and throw it a lot. Under no circumstances would I consider a man-portable laz cannon "one handed" unless you get your combined size and strength up to 12.
Obscuring fog -> three five meter cubes per caster level that reduce visibility to 2m. Otherwise normal fog that dissipates in about 5 minutes or a dozen flamer shots. I saw this in action against a bunch of 5m tall kill-bots and it worked very well.
Jaunt -> combo-Ok and no other key words, reaction spell usable as a dodge attempt that also teleports you 10m. Line of sight preferred. With a casting DC of 25 you're adding at least 12 to your static defence and you still get the 10m even if you didn't zorp out in time to avoid the hit. Excellent, except...
Porte: This is almost exactly like having a portal gun. If you can't have terrible abusive fun with this you aren't even trying. Half action or reaction to cast, lasts a day per caster level (odd but... ok?). 100m range, line of sight required, also a sufficiently large and reasonable flat surface to cast it on. It can't move, neither the portal nor the surface. It just winks out if that happens. You'll have to cast the spell twice and can't have more than 2 portals.You can't dismiss it but if you cast another you choose which one winks out. People/things can hang out half way through but you can't cut them in half, they're safely ejected. Momentum is conserved. Now I, personally, interpret the 'no move' clause as the portal target surface can't be moving relative to the caster during casting and can't move relative to the other portal. So casting in two different cars on a moving train works fine, until the train rounds a bend and the forward portal winks out. Seriously, portal gun.
Cloudkill -> as fog cloud but you only get one 5m cube per caster level. Anyone who breathes within it has to make a DC 15 constitution save or take a wound, unless they're immune in one of at least 5 different ways. One star, would not cast again.
Greater servant -> as lesser servant but with a higher cast DC and 4s in all stats and skills. 8 HP, 5 resilience, static defence 26, rolls 8k4 for everything, punches for 4k1 damage or hand it a big axe for 7k3 and 4 penetration. A legit moderately dangerous & useful critter.
Teleport -> combo-ok blink without a maximum distance. Only to places you've "seen" and perception+wisdom vs. 25+ to get somewhere that isn't "very familiar". Can't go through crystal spheres, void shields, or probably other force fields. Notably not multi-target and not a touch spell. Still quite good.
Incendiary cloud -> as fog cloud but three 5m cubes per level and doesn't care about the flamers. Anyone entering or being inside gets automatically set on fire. Better but not good enough.
Gate -> social (not in combat). As Porte but you don't need line of sight, uses the teleport rules for non-LOS targeting. And that's it... The "as Porte" just ruins it. It's really really disappointing for a 5th level spell. My personal errata: cast non-combat it takes an hour but has teleport range and doesn't worry about the ends moving relative to each other. Still can't go through crystal spheres or shields. Cast in combat it's a full round and has the 100m range limit but you get both portals at once.
Black blade of disaster -> basically summon a power sword with infinite armour penetration that winks out if you drop it. Lasts through the scene. Not good enough to take. Just a power sword with better penetration isn't impressive. Doesn't say "pinnacle of conjuration spells" to me. I'd at the minimum add shocking and a fear test (DC = to-hit roll), possibly even toxic.

Personal ratings
L1: Blink. Sorry. Web needs more details and invisible servant just can't compete.
L2: Tough choices. Although I'd only take lesser servant if I'm not expecting to get Conjuration 4 anytime in the next 3-6 RL months.
L3: Porte unless I'm totally desperate for dodge actions. Even then since it's also a reaction you can conceivably stunt it into a quasi-dodge if you've prepared correctly. Not cloudkill, it's far too weak.
L4: Not incendiary cloud. The other two are both really good.
L5: Not in a by-the-book game or else take the other L4 spell. Using my versions... probably gate. Ooch, just looked up the D&D 3.5 black blade spell, I'd forgotten it was functionally a disintegrate+ flying, dancing, sword. I'll have to think about my errata version a bit more. But seriously it needs to be more then a 4k2 sword that only ignores armour.

Know why this is such a popular magic school? Blink. It's just too good to pass up at first level. You could very nearly justify dropping cloudkill to 2nd, and obscuring fog to 1st, then putting blink at 3rd and it would still be pretty good. Even just swapping blink and obscuring fog might be enough.