Aftershock is the general "go-to" choice in most cases, there honestly isn't a bad match up to take it in. There some match up where you can afford to be a little greedy with damage, but opting for Aftershock is never strictly a bad idea.

Aery as a keystone is pretty garbage honestly, but the Sorcery minor runes are really strong on Singed. Opting for Aery, in my opinion, is less about the early game damage you get (which is nice but nothing to write home about) and more about investing into either scorch for better all in potential (meh) or the insurance policy of Gathering Storm (I'm a fan atm).

Spellbook is the best choice if you're looking to snowball; flash + ignite is not something a lot of people know how to play around when against Singed, or at the very least they don't expect it. Minion Demat is insanely strong right now since the minon HP changes, and provides an excellent trump card in establishing lane priority.