In my experience?
I've had the 2.8/24 Ai for a long long time; can't remember when I bought it used, or for what price. '85? Great little lens, use it anywhere.
Just acquired the 2.8/28 Ai-S in as new condition, at an undisclosed price. This is a really fantastic piece of glass; still difficult to focus in a dimly lit bar using an F2AS.
I have the 1.8/50 Ai (wanted the 2.0, didn't get it), great lens. Simple. Good. Use it everywhere.
1.4/50 Ai-S is very good, you have to accept a little softness wide open.
1.2/50 Ai-S (bought it new for eur 440). A gem. Period. Use it wide open, it gives sharp low contrast a whole new meaning. Get it!
2.5/105 Ai-S, I wish I'd never sold it. The 2.0/85 Ai-S is pretty compact and no slouch either. Great portrait lens. Consider it?