Thisis very personal, very much dependant on the commenter's lineup, and dependant on the purpose the lens is used for.
The FA 50 macro is my sharpest lens. But it's a bit too sharp for portraits.
The DA 21 LTD is amazing for subject isolation, because of the 3D effect it creates, even though the bokeh is more busy than the macro. Its performance is more even across the frame, too.
The F50 f1,7 is king of low light. My favourite in this kind of situation.
The M150 has that nice M feeling, plus its my only fast tele. So it's my favourite tele prime
One lens, one purpose.
I could even say without shame that the 18-55 WR is my favourite hiking lens, since it's small, weather proof, light, and reliable. But it's not my best lens.