Most played cards in Humans:

4 Decks
Noble Hierarch
12 copies - 3 average
Thalia, Guardian of Thraben
12 copies - 3 average
Aether Vial
12 copies - 3 average
Unclaimed Territory
12 copies - 3 average
Mother of Runes
12 copies - 3 average
Cavern of Souls
12 copies - 3 average
Thalia's Lieutenant
11 copies - 2.75 average
Wasteland
11 copies - 2.75 average
Ancient Ziggurat
11 copies - 2.75 average
Champion of the Parish
11 copies - 2.75 average
Kitesail Freebooter
10 copies - 2.5 average
Meddling Mage
10 copies - 2.5 average
Horizon Canopy
6 copies - 1.5 average
Karakas
6 copies - 1.5 average
Reflector Mage
6 copies - 1.5 average
Mantis Rider
6 copies - 1.5 average
Phantasmal Image
5 copies - 1.25 average
Surgical Extraction
4 copies - 1 average
Imperial Recruiter
4 copies - 1 average
Palace Jailer
3 copies - 0.75 average