What is the sharpest lens you own?

I think my sharpest lens is the Sigma 150/2.8 none OS, anything you shoot with this lens turns into a piece of art, extremely sharp at 2.8,high contrast and beautiful colors,  my 300 2.8 IS has the same sharpness, but I don't use it as much as the Sigma, followed by my 70-200/4 IS, then my sharp copy of 24-70/2.8L

But for my surprise I bought a Canon EF 28-70 /3.5-4.5 II from garage sale for $40, sharpness wise this is almost perfect, extremely sharp corner to corner in any focal length,and I am a pixel peeper,  it is sharper than the 17-40/4L and 17-55/2.8 that I previously owned, but built quality is very funny, every time I use it I think it is the last time and it is going to fall a part, very slow and noisy auto focus, but accurate, that is why I am looking for another copy of this lens.