Most played cards in UWR:

2 Decks
Counterspell
8 copies - 4 average
Swords to Plowshares
8 copies - 4 average
Tundra
8 copies - 4 average
Psionic Blast
8 copies - 4 average
Disenchant
8 copies - 4 average
Volcanic Island
8 copies - 4 average
Lightning Bolt
8 copies - 4 average
Serendib Efreet
7 copies - 3.5 average
Chain Lightning
7 copies - 3.5 average
Black Vise
7 copies - 3.5 average
Mishra's Factory
7 copies - 3.5 average
Red Elemental Blast
6 copies - 3 average
Blue Elemental Blast
6 copies - 3 average
Savannah Lions
4 copies - 2 average
Plateau
3 copies - 1.5 average
Divine Offering
3 copies - 1.5 average
City of Brass
3 copies - 1.5 average
Serra Angel
2 copies - 1 average
Spirit Link
2 copies - 1 average
Library of Alexandria
2 copies - 1 average