I'm a control warrior fanboy and I feel like nefarian is better in a super aggro meta, which we aren't really facing. The ideal way you should be trying to use ysera is counting their removal, silences and such (in the mirror match, I love using grom as execute bait) and only playing it when they can't deal with it, so it single-handedly wins you the game.

If you're often finding yourself in matchups where racing and immediate impact is more important, nef is the way to go.