It must be Iridium for me. It has the widest range of oxidation states among all elements, it forms very interesting (and also useful) organometallic compounds (check Vaska's complex), it forms nicely coloured compounds depending on the oxidation state (hence the name, iridium). Being precious due to its low abundance also makes it a pretty neat element. Not luxury-tier, but it can appear as traces in the tips of some luxury fountain pens.
The second place in my heart goes to ruthenium and, after that, I'd say palladium.
