Most played cards in Midrange:

2 Decks
Mishra's Factory
8 copies - 4 average
Tundra
8 copies - 4 average
Swords to Plowshares
7 copies - 3.5 average
Disenchant
7 copies - 3.5 average
Su-Chi
7 copies - 3.5 average
Divine Offering
6 copies - 3 average
Red Elemental Blast
6 copies - 3 average
City of Brass
6 copies - 3 average
Volcanic Island
6 copies - 3 average
Counterspell
5 copies - 2.5 average
Blue Elemental Blast
5 copies - 2.5 average
Lightning Bolt
4 copies - 2 average
Savannah Lions
4 copies - 2 average
Black Vise
3 copies - 1.5 average
Serra Angel
3 copies - 1.5 average
Yotian Soldier
3 copies - 1.5 average
Chaos Orb
2 copies - 1 average
Time Walk
2 copies - 1 average
Balance
2 copies - 1 average
Mox Sapphire
2 copies - 1 average