Most played cards in Madness:

4 Decks
Yavimaya Coast
16 copies - 4 average
Careful Study
16 copies - 4 average
Basking Rootwalla
16 copies - 4 average
Wild Mongrel
16 copies - 4 average
Roar of the Wurm
14 copies - 3.5 average
Arrogant Wurm
13 copies - 3.25 average
Circular Logic
13 copies - 3.25 average
Naturalize
13 copies - 3.25 average
Aquamoeba
13 copies - 3.25 average
Deep Analysis
12 copies - 3 average
Accumulated Knowledge
12 copies - 3 average
Counterspell
12 copies - 3 average
Aether Burst
12 copies - 3 average
Merfolk Looter
11 copies - 2.75 average
Wonder
11 copies - 2.75 average
Tormod's Crypt
9 copies - 2.25 average
Scragnoth
6 copies - 1.5 average
Hydroblast
4 copies - 1 average
Daze
3 copies - 0.75 average
Chill
2 copies - 0.5 average