Uranium but of course! It is the centrepiece of nuclear scientists and engineers’ work, it can help in clean energy production, and it can have numerous other applications besides nuclear power generation, due to its physical (e.g. high density) and chemical (affinity with a large number of chemical elements) properties.
I really like Tungsten. It’s super dense and has the highest melting point of all the elements. It’s a very useful metal in some specific applications, but is still quite rare. And it’s symbol is W, short for ‘wolfram’ – a contender for coolest name surely!
I’m currently listening to an old radio program from the BBC called “Elements” which explains the commercial aspects of each of the elements and so far my favourite has been Titanium. It’s found in a lot of places, is really strong and was traditionally really hard to smelt.
Lead (Pb), in radiation protection it is one of the most used materials. It shields against alpha and beta, and reduces gamma rays. Of course other reactions occur so other shielding material is additionally needed.