Most played cards in Planeswalkers:

1 Decks
Vivid Crag
4 copies - 4 average
Lightning Bolt
4 copies - 4 average
Mutavault
4 copies - 4 average
Rugged Prairie
4 copies - 4 average
Path to Exile
4 copies - 4 average
Hallowed Burial
4 copies - 4 average
Vivid Meadow
4 copies - 4 average
Ajani Vengeant
4 copies - 4 average
Great Sable Stag
4 copies - 4 average
Goblin Assault
4 copies - 4 average
Volcanic Fallout
4 copies - 4 average
Guttural Response
3 copies - 3 average
Firespout
3 copies - 3 average
Reflecting Pool
3 copies - 3 average
Runed Halo
2 copies - 2 average
Obelisk of Alara
2 copies - 2 average
Elspeth, Knight-Errant
2 copies - 2 average
Austere Command
2 copies - 2 average
Armillary Sphere
2 copies - 2 average
Earthquake
2 copies - 2 average