I suggest these decks be tested for 1.321 (This is my personal opinion, from the recommended decks and other decks that have reported good success against the arenas):
Bronze: Unupped Monodark, PvP Grabbow, Rotten Flesh, Mono-Darkness, The Wrecking Ball, Arena Destruction 101 (Steal Mod), Promising MonoLife Bronze Farmer
Silver: PvP Grabbow,
Immorush, Silver Slash (Fully Upgraded), Arena Destruction 101, The Wrecking Ball, The Bone Collector (Pre-1.31 version)
Gold: RoL/Hope (Semi-unupped), New Old Times FG OTK (Both semi-unupped and Upped), The Counter, Day Traitors, Poison Dials SoSac (3 Pendulum mod), Sevs Cremation (Seraph Mod), Tha Gold League Killer V1
Plat: RoL/Hope (Semi-unupped), New Old Times FG OTK (Both semi-unupped and Upped), Poison Dials SoSac (3 Pendulum mod), Sevs Cremation (Seraph Mod), Pestal 101,
Gravity Domination (No pendulum mod)