Which is your most prized lens?

There are many different photographers here in this forum.  From landscape/buildings, street/portrait, animals-birds/sports shooters, we all have our favorite lens.  If you could own only one lens you currently have, which one would it be, and why?

Mine is definitely the AF-S 300mm f2.8 VR.   One of Nikon's sharpest, detail, contrast, telephoto sports lens, and with great bokeh for portraits too.

Yes, I want that $9500 AF-S 400mm f2.8G as well.