I have REALLY been enjoying the @MTG_Arena cube this week. The colors are more balanced than I expected, and there are surprisingly few duds for a first attempt. Here's a bunch of extremely subjective opinions that folks are welcome to attack viciously:

Top 10 cards to open:

* Elspeth Conquers Death
* Agent of Treachery
* Thassa, Deep-Dwelling
* Kiora Bests the Sea God
* Liliana, Dreadhorde General
* Finale of Eternity
* Embercleave
* Dream Trawler
* Ethereal Absolution
* Ashiok, Nightmare Muse

Honorable mentions (arbitrary, many could be top 10):

* The Eldest Reborn
* Llanowar Elves
* Paradise Druid
* Questing Beast
* Teferi, Hero of Dominaria
* Uro, Titan of Nature's Wrath
* Casualties of War
* Garruk, Cursed Huntsman
* Karn, Scion of Urza
* Golos, Tireless Pilgrim

First 20 cards I'd cut (because awful), 1/2:

* Board the Weatherlight
* Mace of the Valiant
* Zetalpa, Primal Dawn
* Bond of Insight
* Favorable Winds
* Tetsuko Umezawa, Fugitive
* Cauldron Familiar
* Duress
* Lotleth Giant
* Nightmare's Thirst

2/2:

* Piper of the Swarm
* Sword-Point Diplomacy
* Blood Aspirant
* Fires of Invention
* Fiery Cannonade (don't need this AND Flame Sweep)
* Squee, the Immortal
* Chainweb Aracnir
* Flaxen Intruder
* Kronch Wrangler
* Vivien's Arkbow

Actually, here's 10 more:

* Savvy Hunter
* Sky Terror (worse than Relentless Raptor, I think)
* Crucible of Worlds
* Entrancing Lyre
* Gleaming Barrier
* Gingerbrute
* Sparring Construct
* Witch's Oven
* Field of Ruin
* Labyrinth of Skophos

I want to see more midrange/control artifacts, more enchantments, and more Izzet instants/sorceries for those archetypes.

Specific card suggestions to follow for each color:

White:

* Ancestral Blade
* Bounty Agent
* Healer's Hawk
* Hero of Precinct One
* Kenrith, the Returned King
* Martyr of Dusk
* Master Splicer
* Pride of Conquerors
* Raise the Alarm
* Ranger of Eos
* Shalai, Voice of Plenty
* Tithe Taker
* Territorial Hammerskull

Blue (1/2):

* Callaphe, Beloved of the Sea
* Callous Dismissal
* Departed Deckhand
* Essence Scatter
* Faerie Vandal
* Mu Yanling, Sky Dancer
* Mystic Archaeologist
* Nightveil Spirte
* Omen of the Sea
* Quasiduplicate
* Secrets of the Golden City
* Shimmer of Possibility

Blue (2/2):

* Drawn from Dreams
* Dream Eater
* Mesmerizing Benthid
* River's Rebuke
* Sphinx of Foresight
* Storm Fleet Spy
* Syncopate
* Wizard's Retort

Black (1/2):

* Burglar Rat
* Davriel, Rogue Shadowmage
* Dire Fleet Poisoner
* Lazotep Reaver
* Macabre Waltz
* Mire Triton
* Pestilent Spirit
* Phyrexian Scriptures
* Ravenous Chupacabra
* Rite of Belzenlok
* Seeker's Squaire
* Stitcher's Supplier
* Tymaret Calls the Dead

Black (2/2):

* Champion of Dusk
* Divest
* Twilight Prophet

Red:

* Chandra, Fire Artisan
* Devouring Hellion
* Dismissive Pyromancer
* Haphazard Bombardment
* Heartfire (seems better than Fling)
* Irencrag Pyromancer
* Krenko, Tin Street Kingpin
* Rix Maadi Reveler
* Rowdy Crew
* Star of Extinction

Green:

* Adventurous Impulse
* Carnage Tyrant
* District Guide
* Merfolk Branchwalker
* Might of the Masses
* Multani, Yavimaya's Avatar
* Nightpack Ambusher
* Nullhide Ferox
* Return of the Wildspeaker
* Ripjaw Raptor
* Territorial Allosaurus
* Vivien Reid
* Wildborn Prserver

Gold (1/2):

* Angrath, the Flame-Chained
* Cruel Celebrant
* Deathsprout
* Discovery/Dispersal
* Domri, Chaos Bringer
* Doom Foretold
* Dovin, Grand Arbiter
* Elite Guardmage
* Ral's Outburst
* Sorin, Vengeful Bloodlord
* The Royal Scions
* Thief of Sanity

Gold (2/2):

* Emmara, Soul of the Accord
* Hadana's Climb
* Hero of the Nyxborn
* Heroic Reinforcements
* Ironroot Warlord
* Knight of the Reliquary
* March of the Multitudes
* Ravager Wurm
* Regisaur Alpha
* Swiftblade Vindicator
* Trostani Discordant

Artifacts and lands:

* Azor's Gateway
* Bag of Holding
* Mana Geode
* Memorials to (Folly, Genius, Glory)
* Orazca Relic
* Skittering Surveyor
* Transmogrifying Wand