Progress bar "pulse" method indicates that something has been done. For example, when indexing files, it can indicate that one file has been processed, but the number of files to process is unknown. In case of ad-hoc commands, there is only an indication that Gajim is waiting for the network, so spinner is more appropriate here.
Radio buttons are more suitable for static lists of options.
GNOME seems to be using lists in similar situations, for example to show a list of network printers.
This also makes it possible to search a command by typing.