Mine is Burning-Tree Emissary

I'm going to have to go with either Lazav or Prime Speaker Zegana... both of whom are just nasty and have potential to affect the meta.

I like Burning Tree Emissary for it's essentially free casting cost...
Also, I like these for their power in limited...
and

Blind Obedience seems a bit overpowered to me with it also having Extort. It could see some play in standard and possibly modern with it eliminating both Haste and Artifacts as immediate threats. Since it targets artifacts, it renders same-turn rune-key and artifact land use ineffective.

I'm hoping there will be some decent enchantment removal in the set. Otherwise, I'll probably be playing GRW.
I really want to like Semic... I'm hoping their offerings round out as the spoilers continue (Currently, my favorite Semic is Zameck Guildmage, but don't see it getting much play outside of limited and EDH).

New favorite spell, !
So versatile!!! Definitely want to play GRW!