Most played cards in UR:

4 Decks
Volcanic Island
16 copies - 4 average
Counterspell
16 copies - 4 average
Red Elemental Blast
15 copies - 3.75 average
Serendib Efreet
12 copies - 3 average
Lightning Bolt
12 copies - 3 average
Chain Lightning
12 copies - 3 average
Shatter
10 copies - 2.5 average
City of Brass
10 copies - 2.5 average
Mishra's Factory
10 copies - 2.5 average
Psionic Blast
8 copies - 2 average
Strip Mine
8 copies - 2 average
Energy Flux
7 copies - 1.75 average
Blood Moon
7 copies - 1.75 average
Fireball
7 copies - 1.75 average
Blue Elemental Blast
6 copies - 1.5 average
Earthquake
5 copies - 1.25 average
Ivory Tower
4 copies - 1 average
Fellwar Stone
4 copies - 1 average
Library of Alexandria
4 copies - 1 average
Shivan Dragon
4 copies - 1 average