Say you do not have any Coin at all but you have just a hundred dollar to purchase a single Silver Coin (graded or not) that you will hold on to your entire life, what would that Coin be? Try to be Sincere and make sure the Coin is at least valued at hundred.
1897 S Barber quarter in VG $125. [hey-- you said at least $100, besides you can probably bargain it down.] 1903 S Barber Dime in G-4, $100.
Hypothetically speaking, if you were only going to by 1 coin in your life, your probably not the kind of person that is going to spend $100 USD on a single coin. Nor would I imagine that you would end up keeping that coin for life.
Well, I wouldn't buy ANY for an investment - BUT, if this is just like a keepsake, or something like that, then most likely I would go with something like a Morgan Dollar, ASE. Both are very popular, and you could get a nice one for less than $100. Speedy
It is a difficult answer though, because you need to acquire the coin for less than $100, but it has to be worth at least $100 or more. Personally I would have said a Morgan also. Funny thing is that a common 1880-P Morgan is the first coin I ever purchased and even if I didn't become a collector I would keep it, because it was minted exactly 100 years before my wife and I were born. We are both born in 1980. But this wouldn't match the parameters because I certainly did not pay $100, and it is definitely not worth $100 (especially because I didn't know the rules of collecting and cleaning and brought it straight home and made it shiny) LOL.