Most played cards in U/R/x Tron:

1 Decks
Giant Solifuge
4 copies - 4 average
Rune Snag
4 copies - 4 average
Annex
4 copies - 4 average
Steam Vents
4 copies - 4 average
Urza's Mine
4 copies - 4 average
Urza's Tower
4 copies - 4 average
Urza's Power Plant
4 copies - 4 average
Remand
4 copies - 4 average
Izzet Signet
4 copies - 4 average
Compulsive Research
4 copies - 4 average
Breeding Pool
4 copies - 4 average
Spell Snare
3 copies - 3 average
Wildfire
3 copies - 3 average
Electrolyze
3 copies - 3 average
Repeal
3 copies - 3 average
Simic Sky Swallower
3 copies - 3 average
Pyroclasm
2 copies - 2 average
Muse Vessel
2 copies - 2 average
Simic Signet
2 copies - 2 average
Demonfire
2 copies - 2 average