Arthur G. Manzo, DDS (retired)

I would recommend Invisalign to close that 3mm gap. It is permanent and relatively quick.  With Invisalign the teeth will be moved and you will have your teeth natural and not filled with material between them that may or may not match shade, size or contour.  Bonding is not permanent and will require redoing sooner or later.

Cosmetic crowns are usually always made of ceramic porcelain, 100%.  Newer boding techniques provide an absolute seal between the tooth and the crown with no leaking or dark lines. They look good and feel like your own teeth.  They can last 20+ years, provided one's bite is stable.  Stabilizing the bite is probably the most important reason high quality cosmetic dentistry can last so long.