Hello,
Dual is not a must for RUTX11. Usually, using the auxhiliary connector is recommended in cases, where signal reception or operator coverage is limited or poor and might provide meaningful improvement. Otherwise, Main connector is sufficient.
Now, comparing your antennas, without knowing, what are the gain, VSWR or radiation patterns of the parabolic antenna is difficult, but it is likely, that that a parabolic antenna will provide better results, as, in general, they are able to detect signals from further distances, offer more gain and their radiation pattern directivity properties are better. However, this also means that you need to have a good idea, of where the cell tower is to align the antenna properly.
Best regards,
