Most played cards in Workshops:

2 Decks
Sphere of Resistance
8 copies - 4 average
Mishra's Workshop
8 copies - 4 average
Wasteland
8 copies - 4 average
Mishra's Factory
8 copies - 4 average
Grafdigger's Cage
8 copies - 4 average
Leyline of the Void
8 copies - 4 average
Phyrexian Revoker
8 copies - 4 average
Ancient Tomb
8 copies - 4 average
Thorn of Amethyst
8 copies - 4 average
Tangle Wire
8 copies - 4 average
Smokestack
7 copies - 3.5 average
Crucible of Worlds
6 copies - 3 average
Dismember
6 copies - 3 average
Ensnaring Bridge
4 copies - 2 average
Inventors' Fair
4 copies - 2 average
The Tabernacle at Pendrell Vale
4 copies - 2 average
Null Rod
3 copies - 1.5 average
Phyrexian Metamorph
2 copies - 1 average
Ratchet Bomb
2 copies - 1 average
Tolarian Academy
2 copies - 1 average