Which complex compound is most stable?

\(\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{3}{\left({\mathrm{NO}}_{3}\right)}_{3}\right]\)

\(\left[{\mathrm{CoCl}}_{2}(\mathrm{en}{)}_{2}\right]{\mathrm{NO}}_{3}\)

\({\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{6}\right]}_{2}{\left({\mathrm{SO}}_{4}\right)}_{3}\)

\(\left[\mathrm{Co}{\left({\mathrm{NH}}_{3}\right)}_{4}\left({\mathrm{H}}_{2}\mathrm{O}\right)\mathrm{Br}\right]{\left({\mathrm{NO}}_{3}\right)}_{2}\)