I got my first and so far only Ai-s 135mm f/2 in a bundle of Nikon MF gear that a daily news shooter dumped when the change shifted to Canon EOS for the tele sports shooting. I admit to not knowing anything about it but the guy said it was a killer volleyball lens. This one was well used but with super smooth focus throw and pristine glass, every shooter shot with a filter but the lens worked way better in those dim gyms without a filter. Indoor volleyball, basketball, baseball from third base, usually a Nikon F3P doing 7fps with MD-4 running over cooked 18v MN-2 Ni-Cads, burning rolls per quarter, fun times. Post news shooting that same lens was my pro secret for weddings. A super deep hood with no filter for first dance with spotlights is what that lens was made to do. Mine suffered a hit to the rear element from a Domke metal strap fitting, the loose clip when working fast and flipping the bag shut. A shatter on that thick element didn't fully chip it but gave a circular shatter, after looking thru the finder the center seemed sharp enough to finish the wedding. The resulting negatives made me regret getting NPS to rebuild the whole thing, helicoids and all, was like a new lens. That lens stayed with me but got melted in the Lahaina wildfires a few years ago, I've considered replacing it but I don't really use that length ofter, and if I did at this stage I'd consider the DC 135mm f/2 just to try it. The original Ai or Ai-s version is also stellar long portraits lens, the natural compromise of the optical design close in gives a lovely glow with sharpness.
I'm also very fond of the 135mm f/3.5 in the compact AI-s version, a really great small lens with a top f-11 performance.