Most played cards in 4c Midrange:

3 Decks
Swords to Plowshares
12 copies - 4 average
Tundra
12 copies - 4 average
Disenchant
12 copies - 4 average
City of Brass
12 copies - 4 average
Mishra's Factory
9 copies - 3 average
Counterspell
9 copies - 3 average
Serendib Efreet
8 copies - 2.67 average
Blue Elemental Blast
8 copies - 2.67 average
Volcanic Island
8 copies - 2.67 average
Lightning Bolt
8 copies - 2.67 average
Red Elemental Blast
7 copies - 2.33 average
Strip Mine
6 copies - 2 average
Serra Angel
6 copies - 2 average
Divine Offering
6 copies - 2 average
Chain Lightning
5 copies - 1.67 average
Control Magic
5 copies - 1.67 average
Fireball
4 copies - 1.33 average
Wrath of God
4 copies - 1.33 average
Savannah Lions
4 copies - 1.33 average
Psionic Blast
4 copies - 1.33 average