Lenses are all pretty much the same at f/8 to f/11 in the sweet spot. Some have a larger range of aperture, though, where they retain sharpness. What are you looking for, though? sharpest wide open? sharpest at a particular stop? sharp on close focused objects? sharp on subjects near infinity? I've not seen a lens that's sharp in every area.
I agree all lenses have a sweet spot, but I find that there is a BIG difference between lenses at the sweet spot:; example my 70-200 VR is much sharper at its sweet spot (actually from 3.5 thru 11) then my 80-400 VR at the sweet spot. Which lens do you consider your sharpest. If you can't limit the answer which lens is your best, which is best wide open, close-up, and at infinity. Thanks for your input. Jack
If you want to know about wide open sharpness and resolution you can compare Nikon's official figures for different lenses with a visit to http://imaging.nikon.com/products/imaging/lineup/lens/index.htm The solid red line (as Nikon explain in the notes) is a good guide to sharpness and the solid blue is a good guide to resolution. The left side is lens center and the right side is extreme corner (for the lens format). Whilst sharpness and resolution requirements are relative to needs it soon becomes apparent that a lens like the 300mm f2.8 at f2.8 is far superior to something like a 20mm at f2.8. There were good optical reasons for the inevitable performance fall of with wide angles. Most Nikon wide angle designs are 20 or more years old and capable of significant improvement if they are ever upgraded. The more recent DX lenses often have better MTF scores than the equivalent cropped areas of the wide angle primes. Results for the recent FX f2.8 primes confirm they are better than the equivalent f2.8 primes - subject to the caveats of size, weight, and for the 14-24 the lack of a front filter thread. There are real world real photographic improvements too. Within minutes of trying the 14-24 on my D3 I took the decision to sell my 14 and 20mm primes. In fairness these primes perform well with film bodies - the sometimes poor results with digital are due to limitations with sensor technology, part cured with the latest D3 firmware upgrade. There is more to lens quality than MTF, but in the context of your question Nikon's MTF is a good starting point.
Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.