Aluminium is the better conductor.
The easiest way to think of Electricity and how it "flows" is use water
in your thinking. Water
flowing through a pipe is just like Electricity. The size of the Pipe will determin how much volume (current) of water can flow. The water pressure (volatge) determines how fast it comes out the end and how far it leaps from the end of the hose.
OK, so if we think of a bolt of lightening as a tank of water being dumped on the ground. Now imagine if the boat of what ever becomes a conductor, is considered a hose. If the pressure and volume is greater than the hose can stand, the hose is destroyed. But maybe the hose is real tuff (steel boat hull), the volume and pressure has to flow through it. But if you add another smaller hose(a person or radio) beside the big strong one, the water will also have enough volume and pressure to want to flow through it as well. So the person can get hurt or Radio
destroyed. If the hose is really big and strong and can take more than the tank can supply in a deluge, then nothing will flow through the smaller one. So the person or Radio
may not feel a thing.
A person on the inside of a vessel may be OK. Even outside, they will remain safe. Providing the material around them can handle the volatge and current
to a far higher degree than the person. The thing the person must be careful of is to not compleate a path from one point of the vessel to another. This would then make them a small hose that some of that water would want to flow through.
Hope this helps those that are, ummm, errr, scientificaly challenged.