The coolest element has to be carbon! There is no other element that can make life possible. It is everywhere and cycles with so much clarity. Organic, inorganic, biochemistry. It is all good.
The coolest element - Phosphorus. Why? Probably due to the way it was discovered. The alchemist, Herman Brand, isolated it by letting buckets of urine sit around and evaporate. It's symbol is "P" - rather appropriate, I might add. You have to admire Mrs. Brand, assuming there was one, for her tolerance of this experiment. Neither my wife nor my mother would have allowed me to do this. Phosphorus proved helpful in creating match heads, so it lived up to its name as a "light bearer."
I very much agree with you with your pick of technetium. I didn't know that it was actually used for anything, but it's been my favorite just because of being the lowest radioactive element.
I think fluorine is the coolest element. It is distinct from the other halogens in how it behaves. It is small but highly electronegative. It is radioactive and show potenital in medicine if it can quickly be incorporated and it is inter in metal catalyzed cross couple. I think fluorine is awesome.
mmmmm... hard to say... I'd say that RHENIUM is the coolest: the last (stable) one to be discovered, one of the most scarce in the universe, nine oxidation states (from -1 to 7!!!) and still no major application!! still a raw diamond!
Coolest, in terms of neat and pretty, is Titanium. I have some earrings that have under gone different heat treatments and the colors are COOL!