Card packs, but I always keep a spare 150 gold if I want to play through an arena run myself. It's fun. It's nice having an extra card pack or two from botting overnight.
Is there a difference? My arena averages in 6.5 wins, and I could never spend all my gold just playing arena........
1st world problems lol As of myself I save it up for the upcoming expansion "Gnomes vs Goblins" cause there will be an entirely new pack of cards which will give you only the cards (most likely only) from the new expansion. They announced there will be 120+ new cards.