An airplane would have a number of advantages over a balloon: * The plane can remain constantly on the sunlit side of the moon and thus in direct communication with the Earth. (At the equator, the plane would have to average just 13-14 km per hour to remain on the sunlit hemisphere.) * While a balloon's flight would be at the whim of the winds, a plane could be directed to specific regions for study. * The plane's design and software could make use of the extensive heritage of design for unmanned aereial vehicles (UAVs) used by the military on Earth. For a platform that will have to operate autonomously for much of the time because of the time delay for commands from Earth, this is a key heritage.
Thing is an airship could manage that velocity and it would still work even if the propulsion system failed. In other words, an airship would work like an airplane except that you have an backup mode as a balloon, if the propulsion system fails.Also Venus looks to be another candidate for this sort of system. You should be able to run a solar powered version.
...Also Venus looks to be another candidate for this sort of system. You should be able to run a solar powered version.