Tough question for me. At this point, my very favorite lenses were from the "old days":

The 90mm for my Leica M4-2. GAWD, what a gorgeous lens: sharp beyond sharp; a great portrait lens.
My Tamron 500 CAT for my Nikons. It made Nikon redesign THEIR CAT. It was sharp, and so much fun to use.
The Kiron 105: sharp as a tack and also focused down to 1:1 macro.
The original Nikkor 80 - 200; Nikon redesigned it to be smaller. HA. It was also less sharp. Mine's a beauty.

I now have a Nikkor 18 - 55, a Tamron 70 -300, and, for kicks, a Rokinon 8mm. Of the three, the Tamron is my favorite. It's also got modest macro capability.

But, lordy, that Leica 90.................