The advantages and caveats of each of the main three conversion methods and consequent fuels are outlined in Figure 3 (as of the time of writing).
Figures 2 and 3 are quite a farsighted response to the Title of this panel discussion - i.e. "marine fuel qualities as they are and will be" with the emphasis on "will be". The future ISO and CIMAC specifications would well include hydrogen and some viewpoints on utilising sun's radiation.
Figure 1 . The tendency is clearly towards electricity as the consumed form of energy.
Figure 2. The total picture of the real "competition" in ships' fuel.