Well, at least it's our favorite ever: "Mother Simpson," the eighth episode from The Simpsons' seventh season, first aired in 1995 and it's a great one.
After faking his death to avoid going to work, Homer goes to the Springfield Hall of Records to clear things up. There he discovers that his mother, who he thought had died when he was a child, is in fact alive. A visit to Mona Simpson's grave reveals it is actually Walt Whitman's; when Homer accidentally falls into his own freshly dug grave, he is berated by a lady who claims he is in her son's final resting place. Homer puts two and two together and, after 27 years, is reunited with his mom.
We won't give away any more of the plot, but "Mother Simpson" manages to be both funny and touching, and along the way, reveals little mysteries, such as the reason for Lisa's intelligence. It also has, arguably, the most poignant finale of any Simpsons episode. A classic.