That's another tough call. One for sure would be the first ever site I detected at an old farm site that was being razed for a commercial development. The barn had fallen in on itself and the house was dozed into a pile of rubble. It looked like the house had burned before it was leveled. But swinging the site was amazing. One particular area I just got to the point of using my pinpointer to keep pulling merc after merc (and 2 Barber dimes). Eventually uncovered a rose glass bowl and lid in the midst. My guess is whoever lived there had been saving those dimes in the bowl, and lost them when the house burned or was torn down burying everything in shallow sand.
The other site I guess would be the site of the first city zoo, now a huge park in a not so good area of the city. I've pulled countless relics, IHs, and silvers including a few Barbers. One big notable was a flax bale seal commonly only found in the UK and to date I believe the only one of it's kind to be found in the US according to the gentleman in England who runs the database logging these seals.