okay i think you should start with a film foil polypropolyne one since its a small value cap... probably cost $5 or less.
or metalised polypropolyne which would cost you $2 or less and neither would sound bad as opposed to some other types you have listed.
...
to get the information to my tweeter i use a couple in parralel for better quality with the larger being film foil and the smaller being a higher quality film foil (if you do this way always just add the two values together and always make the smallest one higher quality as it will be taking the highest frequencies.)
the value you need will depend on the ohm rating of the driver. and of course this will get you a 6 db slope of drop off below whatever value you choose.
also you can put it on the negative or positive leg it makes no difference ( some people think sonically its better to put it on the negative but that that is just to prove their stupidity as a difference isnt a physical possibility
you DONT put this type of filter 'across' the legs
since you want to cross it off at 16khz i would recommend 6db slope as it will not degrade the sound quality as much as 12db or 16db but make sure you tweeter can handle playing half power at 8khz and half again at 4khz... you might wanna cross it of at 20 instead perhaps.
or try this with a cheap tweeter to start with though just to see if it explodes
i can show you a 12 db one later on if you like but got workies now byes!
