Having been detecting for 35 years this is a good questions. I've found all the Barber denominations as well as Seated coinage after finding a seated half dime this year. I've found all the large cent types from 1797-1857 as well as all the 20th century coins. I've found half, one and two reales so far this year as well as NJ, CT, Machins, George II and George III coppers. What would I like to find. How about an 1822 $5 gold piece?
http://images.pcgs.com/CoinFacts/8130_37657492_2200.jpg I know that's not likely so what would I really like to find where the possibility does exist.
1. New England silver piece, shilling, 6 pence or 3 pence.
2. New Jersey copper with date under plow beam.
3. Higley Copper.
4. Connecticut copper with reverse figure facing right.
5. Chain cent.
6. Any bust silver coinage.
I know, I have high hopes, but you never know. I went to check out a new spot for a club hunt last week. After the owner agreed to a club hunt and getting permission I checked the site for about an hour. Dug 10 items to make sure it wasn't going to be a waste of time. One of the first items was a 1782 One Real. The last item was a 1888 Seated Dime. Neither was expected, but you never know. BTW, it should be a great club hunt with over 100 acres to detect.