This is, imo, the best cards in the cube. This is based on how it impact the board, the value it bring to you or the power of the card. (Spoiler : most of the card support Blue, because Blue is fair)

–White–
Ephemerate
Mana Tithe
Battle Screech
Thraben Inspecter
Gideon's Lawkeeper

–Blue–
Counterspell
Mulldrifter
Repeal
Miscalculation
Looter Il-kor

–Black–
Thorn of the Black Rose
Pestilence
Hymne to Tourach
Falkenrath Noble
Chittering Rat

–Red–
Lightning Bolt
Hissing Iguanar
Vulshok Sorcerer
Fireblast
Kiln Fiend

–Green–
Llanowar Elves
Moldervine Cloak
Sarulf's Packmate
Rancor
Primal Huntbeast

–Colorless–
Porcelaine Legionaire
Vulshok Morningstar
Serrated Arrows
Prophetic Prism
Pristine Talisman

–Gold–
Fire//Ice
Dinrova Horror
Agony Warp
Wavesifter
Jilt

–Land–
Izzet Boilerwork
Dimir Aqueduct
Ash Barren
Thriving Isle
Shimmerdrift Vale