Here are my picks for best cards in each color/category:
Blue: Psionic Blast , Teferi, Ancestral Vision .
Psionic Blast is just nuts in U, Teferi can wreck havoc to control decks and Ancestral Vision will see regular play due to being a very powerful card drawer in the format.
Black: Plague Sliver, Smallpox
Juzam like Plague sliver just means some beatdown, while smallpox
Green: Call of the Herd, Stonewood Invocation
Not much to say about COTH: beatdown all the way.
Red: Jaya Ballard, Sudden Shock
Jaya can adapt to toast her enemies while Sudden shock allows you to deal damage without being interrupted.
White: Magus of the Disk, Serra Avenger
Cast Motd, wipe board, cast Serra Avenger.
Land: Gemstone Mine, Terramorphic Expanse