Which black shade is best for my project?

Benjamin Moore Black 2132-10 is Benjamin Moore's darkest neutral black (has no undertones, but can look a bit blue under toned in cool/north facing lighting) 

Onyx (a warm black) is Benjamin Moore's most popular black (warm undertones, no blue undertones) 

Black Panther- no undertones, but a softer black than 2132-10.

Black Satin- blue undertones in many lighting situations, softer black 

Black Iron- cool undertones, softer black

Wrought Iron- a soft grey-black
 

What sheen is best for my furniture?

 For a traditional or maximalist vibe, I generally recommend satin or semi gloss.  For an organic modern or boho look, a matte sealer makes the black paint look a little lighter and a bit less formal.