Antz - October 2, 1998
A Bug's Life - November 25, 1998
Many copycat movies are a product of pure coincidence - two studios just happen to be working on similar stories. However, that's not the case with the animated films Antz and A Bug's Life. The similarity of the two films - which each tell the story of an ant bucking the expectations of his colony to choose his own path - led to a well-documented falling out between Dreamworks' Jeffrey Katzenberg and Pixar's John Lasseter - with the latter accusing the former of idea theft (Katzenberg had left Disney a few years prior).
Despite the acrimony between Dreamworks and Disney, both films actually fared well with both critics and audiences. A Bug's Life was the bigger box office success, earning over $360 million to Antz' $170 million. However, Antz earned a slightly higher Rotten Tomatoes score (95% vs. A Bug's Life's 92%).
While they tell similar stories, Antz and A Bug's Life are light years apart when it comes to tone. Personally, I like the sharper, satirical humor of Antz to the more kid-friendly A Bug's Life. However, if we're going based on critical and financial success, the winner has to be Pixar.
Winner = A Bug's Life.