Banana #1. You're not accounting for the payload capability.
And in $/Wh terms, it's quite the opposite trend:
Spark: $2.90 / Wh
MP : $2.04 / Wh
P4P : $1.89 / Wh
Inspire : $1.63 / Wh
Further, the MP, P4P and I2 have similar efficiency at 458, 467 and 458* gram-minutes per Wh
But...