Most played cards in 4 Color Control:

3 Decks
Sakura-Tribe Elder
12 copies - 4 average
Birds of Paradise
12 copies - 4 average
Plow Under
11 copies - 3.67 average
Sword of Fire and Ice
11 copies - 3.67 average
Naturalize
10 copies - 3.33 average
Engineered Explosives
9 copies - 3 average
Boil
9 copies - 3 average
8 copies - 2.67 average
Sowing Salt
8 copies - 2.67 average
Eternal Witness
8 copies - 2.67 average
Circle of Protection: Red
7 copies - 2.33 average
Blinkmoth Nexus
7 copies - 2.33 average
Mana Leak
6 copies - 2 average
Trinket Mage
6 copies - 2 average
Etched Oracle
6 copies - 2 average
Meloku the Clouded Mirror
5 copies - 1.67 average
Condescend
4 copies - 1.33 average
Wood Elves
4 copies - 1.33 average
Fireball
4 copies - 1.33 average
Troll Ascetic
4 copies - 1.33 average