Which enforcer lineups give most experience gain for each kingpin?

You can't control how much experience your enforcers get from challenging kingpins no matter what lineup you use. By nature, enforcers at a lower level will always receive less EXP than the enforcers at a higher level. But that's only because it takes less EXP to rise to the next level at lower levels. At higher level it will take more EXP, so it kind of balances out and equals the same either way