TOD:
In college, it was definitely Hearts, and even during the early years of my first partnership, we used to have card night with friends every Tuesday, and we played Hearts. Really enjoyed those evenings.
Now, if I'm asked to play cards, I'd rather play gin rummy.
I used to play Bridge (learned how on my first computer), but I haven't played in so long I've forgotten almost everything about the bidding.
Simplier games like Old Maid, Go Fish, and Battle are also favorite memories from my youth.