I have seen different keystones ran on Poppy but I can't figure out which is best.
The three that I have kind of narrowed it down to are Grasp, Aery, and Conqueror.
In my honest opinion I feel like the resolve tree in general is better to give her more tankiness.
Why is there a downvote for a gameplay question...
I use aftershock.
Aftershock and Grasp Imo are the best ones. Aftershock is better vs most ranged matchups, and grasp is better vs most melees. I haven't really tried aery/conqueror much, but poppy's split pushing is overall weaker than most other skirmisher/fighter champs. Imo, grasp is a better aery when built tank/bruiser.
you could cheese and go electrocute
Phase Rush and Aftershock are by far the best. Grasp doesn't proc much on Poppy. Aery is iffy and is just a tad more damage (can't shield anyone..... would be better off with Comet)
Conquerer's an interesting pick, but offensive Poppy doesn't generally stay in the fight long enough to abuse it. She In - outs.
I'm a move speed addict.
On Poppy I'm literally using Sorcery/Inspiration just to URF her Q. The CDR/Move speed also work well at getting her W out more, and getting around the map.
But....... that's because I'm used to short engagements, and getting the hell out. Someone who likes to stay in and be risky..... go Aftershock. Will proc every time she wall knocks or even E's, so it's really good.
Aftershock stacks with her w passive
Koreans take aery
Aftershock vs range champs in lane.
Grasp vs Melee champs in lane.
Electrocute if jungle.
Grasp has good synergy with her passive
instead of telling you keystone i will tell you my complete runes. i played poppy on ranked now i have about 52.8 % winrate and won 9/10 first games as her. if you manage to win lane roam a lot, if you see mid is about to take turret and you have pushed your lane enough to leave it, go push midlane and kill the enemy if he is there, in case he is focus him not pushing. anyway back to runes!
now these are the runes i use
now if you are interested more in depth i can also tell you my items. this is my build:
first item: 
core build
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-> 
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-> 
(or 
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Poppy is really matchup dependant. I use to run resolve tree on her, but the stats it gives are so fucking bad against the bruiser meta that I can't reccomend it.
Go Arcane Comet and do your Camille impression with Q trades Electrocute against someone like Garen who needs to be all-in'd Aery if you want to poke with her passive
Nothing else is really worth it. She can try for a kleptomancy strategy throwing out a Q->P, but her struggles in lane aren't related to sustain in the first place so it doesn't help much.
I decided to go with Grasp for one specific reason. Lane sustain and sustain in long extended fights. Poppy has almost no sustain and this lets her keep trading in lane without losing out on health.
