About 50 years ago, my grandmother gave me a couple of bags of coins she had accumulated, all from circulation. My favorite would have to be an 1838 Gold Quarter-Eagle in AU. A close second would be the set of 35 different year Indian Head Cents, mostly MS RB and BN but some AU (no keys). Alas, the whole works, including everything else I had accumulated was stolen in 1980, but my current interest was fueled by her gift.
For me it was a MS-65 1955 Doubled Die Lincoln cent, at a coin show last year. Man what a beautiful coin!