From least to most efficient:

Steel Scorpion (V3): 0.9 star chips per duel
Hourglass of Courage: 1.2
Sparks (Seto SA): 1.2
Cursebreaker (V1 SA): 1.2
Great Bill: 1.5
Takuhee: 1.8
Toon Alligator: 1.8
Greenkappa: 2.2
Jirai Gumo: 2.9
Muse-A (V3): 3.5
Parrot Dragon: 4.2
Rude Kaiser: 4.7
Living Vase (V3): 4.8
Tongyo: 5.3
V1 cheapest rares: 8.8
Kaiba cheapest rares: 8.8

Jono 1 farm starts at 4.4