I'm a cranky old bugger so take that into account. I have bought and eventually sold almost all the newer AF Nikkor lens I wanted to use. Their specialty wideangles are great, the others suffered from terrible fringing and flare. On the other hand my old prime Nikkor MF lenses some of which I bought in the 70's are still stellar performers. I am not sure if Canon etc. suffer from the same QC issues like Nikon but I have found both old and new lenses have quite a variation in quality from lens to lens. I tested several lens of each FL before actually buying.
I loved my Nikkor 2/28 and later found that the 2.8/28 Ais beats it at the borders at every stop they share. My AFS 1.8/28mm is even better with less coma and CA. Same story at 20mm were I started with the UD 3.5 tested the 2.8/20mm and finally settled on the marvellous 2.8/21mm Distagon ZF. At around 50/55mm to me it is more about character than anything else. You will hardly find the best lens at this fl in general but I would leave out the 2.8/45mm P wich was quite a step behind in any respect.
I basically don't have new lenses so I can't really compare and thus don't take my opinions seriously. I read in many forums that older lenses are so poor that they don't have sufficient sharpness for today's imaging sensors. But I feel that new lenses are not better because most of the improvements are for better automation. Setting aperture automatically and faster auto focus. Newer lenses tend to exhibit more focus breathing due to their internal focusing design. I don't know if this is good or bad but I don't like that with my lenses.
As an addendum to my first comment I use a Nikon D700 for my commercial work. The old lenses are plenty sharp. For film work I use a Nikon F5 and N90s.