Most played cards in 4c:

1 Decks
Polluted Delta
4 copies - 4 average
Force of Will
4 copies - 4 average
Scalding Tarn
4 copies - 4 average
Deathrite Shaman
4 copies - 4 average
Brainstorm
4 copies - 4 average
Ponder
4 copies - 4 average
Hymn to Tourach
4 copies - 4 average
Snapcaster Mage
3 copies - 3 average
Underground Sea
3 copies - 3 average
Baleful Strix
3 copies - 3 average
Kolaghan's Command
2 copies - 2 average
Pyroblast
2 copies - 2 average
Misty Rainforest
2 copies - 2 average
Jace, the Mind Sculptor
2 copies - 2 average
Diabolic Edict
2 copies - 2 average
Fatal Push
2 copies - 2 average
Thoughtseize
2 copies - 2 average
Spell Pierce
2 copies - 2 average
Surgical Extraction
2 copies - 2 average
Volcanic Island
2 copies - 2 average