Answer
The isothermal process has the most work done, and the adiabatic process has the least work done.
Work Step by Step
We know:
$dQ = dU + dW$
We look for the greatest/smallest change in $dW$. In the isothermal situation, $dU$ equals zero, so we see that all of the energy is turned into work. For the adiabatic situation, $dQ$ equals zero. When this is plugged into the equation, it follows that it is actually the system doing the work, meaning that negative work is done on it. Finally, in the isobaric situation, there is no change, so no work is done. Therefore, the isothermal process has the most work done, and the adiabatic process has the least work done.
