Semisolid media such as MIO are used to determine motility. Another such medium such is SIM (sulfide, indole, motility) medium. When would you use SIM instead of MIO?
In this specific scenario, seeing since both of the mediums are differential, the bacteria can grow on either of them, therefore either of them would be a good choice. A differential media allows the researcher to visually distinguish which species have the specific biochemical process. Which in this case both options have the ability to allow bacteria to grow which is what is needed.