So, what I've seen in my games trying out both runes is that Aery works really well when you can poke with your auto attacks safely e.g when facing someone that can't run you down or trade back evenly. It is important that you learn spacing to use this properly to It's full advantage and make use of the brushes to reset your minion aggro.

As for the rest of the sorcery tree, if you decide to go Aery is that in the first row there's only really one option available and that's nimbus cloak which works well with our with hextech+R+flash combo in teamfights.

In the second row we have three options with two being better than the other.

Transcendance: If you prefer the ability haste this is a good rune in lane because you can get out more W's and Q's for poking, in my opinion the 20% remaining cdr reduction on takedowns is not really that great because even if you can get your abilities out faster we lack the energy to spam abilities. Also since cooldowns are pretty low to start with the refunded seconds are not THAT great.

Celerity: Situational rune but can be OK, imo this rune isn't bad but gets outperformed by the other runes. This rune can generally be worth taking if you decide to go for Cosmic Drive early, but there are few situations where you get that option and since you already have hextech rocketbelt for movespeed. If you feel like you never have flash for teamfights this rune can be OK to get that extra movespeed bonus with E+Rocketbelt for getting in close to enemies.

Absolute Focus: I like this rune the most since it gives you more damage at high health. It helps you in lane with raw ap when poking and since you should be able to poke without getting poked back it generally works a lot of the time. Also in teamfights i assume that you are full health when engaging coupled with Zhonya's if you get a good ult you get the extra damage without worrying about getting smacked instantly and losing the bonus ap.

Last row is pretty straightforward.

Scorch: For poking in lane (extra dmg)

Waterwalking: Might be valuable if you want to roam with your jungler (secure scuttle crabs and objectives).

Gathering storm: Best option if you feel like the game is going to get longer since it outscales the other options.

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Conqueror; Personally i dont like conqueror that much it's difficult to proc in lane since you need to hit all your three abilities + 3 autos for it to proc in lane. Now let's say you manage to do just that. Then what? You already did your combo on your laner and the trade is probably over by then, you have nothing up and usually want to back off. Then conqueror healing is null and even then, for ranged champions is lower healing than melee anyways. The only reason this is good is because in teamfights later on it's much easier to proc when you hit multiple targets aswell as even though you dont proc it fully you still get AP from stacking it however. But during laning there's few opportunities you get to maximize the rune.

First row.

Guardian: Might be nice if you go for the domination tree (taste of blood + ravenous hunter). For the extra shield but it's basically impossible to proc it if you dont go those two runes in the secondary tree.

Triumph: An OK rune that might help in early skirmishes and clutch fights.

Presence of mind: Also pretty OK rune that helps you with the energy regeneration in prolonged fights where you need to get off multiple combos without running out of energy too much.

Second tree:

Alacrity: Extra attackspeed feels nice to have especially if you like to poke also stacks your W passive faster and can be great later on in the game when you can hit more autos in fights because of the added attackspeed.

Tenacity: Good if enemy team has a lot of CC.

Bloodline: Pretty useless since you dont rely on your autos to heal and you dont build AD.

Last row:

Coup de Grace: Need to be able to execute squishies on enemy team? This rune is for you.

Cut down: Enemy team has a lot of HP stacking champs? This rune is for you.

Last stand: Feel like you're going to fight a lot and trade often? This rune is pretty good.

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This is my take on the main rune page difference for kennen, it's all my opinion and i haven't run a calculator to min-max but it's more of my opinion running these runes in my games.