Most played cards in Inside Out:

5 Decks
Snow-Covered Island
35 copies - 7 average
Inside Out
20 copies - 4 average
Tireless Tribe
20 copies - 4 average
Dispel
19 copies - 3.8 average
Circular Logic
18 copies - 3.6 average
Brainstorm
18 copies - 3.6 average
Shadow Rift
18 copies - 3.6 average
Ponder
18 copies - 3.6 average
Augur of Bolas
16 copies - 3.2 average
Evolving Wilds
15 copies - 3 average
Ash Barrens
15 copies - 3 average
Preordain
15 copies - 3 average
Seeker of the Way
14 copies - 2.8 average
Journey to Nowhere
9 copies - 1.8 average
Standard Bearer
8 copies - 1.6 average
Frantic Inventory
8 copies - 1.6 average
Prismatic Strands
8 copies - 1.6 average
Gigadrowse
7 copies - 1.4 average
Hydroblast
6 copies - 1.2 average
Snow-Covered Plains
6 copies - 1.2 average