I’m interested to see whether or not Day’s Undoing further increases Affinity’s share of the metagame after origins.

My bet is that it will.

I think Amulet Bloom is the better option right now. Both decks are equally strong, with a slight edge to Grishoalbrand, against opponents who can’t get that turn 1-3 interaction. But against opponents who are trying to interact and do have their hate cards, Amulet Bloom is going to be better. For Bloom, it’s really just Moon you have to worry about, and even then you can get around that with smart plays and deckbuilding (e.g. Coalition Relic in the board). For Grishoalbrand, you have to worry about both the graveyard hate and the countermagic, and from what I’m seeing in the Prelim lists there’s way more of that than there is Moon.

That said, I would personally pick Grishoalbrand because I’m better with the deck. But assuming you know both about equally well, Amulet seems better.