Most played cards in UW:

1 Decks
Tundra
4 copies - 4 average
Serra Angel
4 copies - 4 average
Serendib Efreet
4 copies - 4 average
Counterspell
4 copies - 4 average
City of Brass
4 copies - 4 average
Disenchant
4 copies - 4 average
Swords to Plowshares
4 copies - 4 average
Blue Elemental Blast
3 copies - 3 average
Circle of Protection: Red
3 copies - 3 average
Mishra's Factory
3 copies - 3 average
Underground Sea
2 copies - 2 average
Jayemdae Tome
2 copies - 2 average
Moat
2 copies - 2 average
Dust to Dust
2 copies - 2 average
Recall
1 copies - 1 average
Time Walk
1 copies - 1 average
Sol Ring
1 copies - 1 average
Spirit Link
1 copies - 1 average
Psionic Blast
1 copies - 1 average
Timetwister
1 copies - 1 average