Most played cards in Midrange:

3 Decks
Volcanic Island
10 copies - 3.33 average
City of Brass
10 copies - 3.33 average
Red Elemental Blast
10 copies - 3.33 average
Blue Elemental Blast
9 copies - 3 average
Mishra's Factory
9 copies - 3 average
Lightning Bolt
8 copies - 2.67 average
Tundra
8 copies - 2.67 average
Disenchant
7 copies - 2.33 average
Su-Chi
7 copies - 2.33 average
Swords to Plowshares
7 copies - 2.33 average
Divine Offering
6 copies - 2 average
Psionic Blast
6 copies - 2 average
Underground Sea
6 copies - 2 average
Counterspell
5 copies - 1.67 average
Earthquake
5 copies - 1.67 average
Chain Lightning
4 copies - 1.33 average
Sedge Troll
4 copies - 1.33 average
Azure Drake
4 copies - 1.33 average
Hypnotic Specter
4 copies - 1.33 average
Savannah Lions
4 copies - 1.33 average