All of Nikon 180mm f/2.8's are fine lenses, but at current prices I suggest going with an ED version. While it's by no means a fragile lens, a lot of 180mm's saw professional use, with all of knocks and bumps that goes along with such use. Don't buy without a return privilege and shoot a sample roll as soon as you receive the lens.
OTOH, I've seen quite a few "closet queen" 200mm f/4's of all types. It's a wonderful lens to use "in hand," but at f/4 and f/5.6 chromatic aberration can get a bit intrusive. Watch out for fungus, though.
The only Nikon 20mm lenses I've used are 20mm f/2.8's. Both the AI-s and AF versions use the same optical formula, and each is a good performer especially at middle distances. But each also has noticeable barrel distortion with a bit of a mustache "kicker."