Most played cards in M:

1 Decks
Gideon, Ally of Zendikar
4 copies - 4 average
Unlicensed Disintegration
4 copies - 4 average
Concealed Courtyard
4 copies - 4 average
Inspiring Vantage
4 copies - 4 average
Release the Gremlins
4 copies - 4 average
Spire of Industry
4 copies - 4 average
Fatal Push
4 copies - 4 average
Aether Hub
4 copies - 4 average
Scrapheap Scrounger
4 copies - 4 average
Toolcraft Exemplar
4 copies - 4 average
Thraben Inspector
4 copies - 4 average
Walking Ballista
3 copies - 3 average
Archangel Avacyn
3 copies - 3 average
Fumigate
3 copies - 3 average
Heart of Kiran
3 copies - 3 average
Nahiri, the Harbinger
2 copies - 2 average
Skysovereign, Consul Flagship
2 copies - 2 average
Shock
2 copies - 2 average
Needle Spires
2 copies - 2 average
Eldrazi Displacer
2 copies - 2 average