The Uncanny X-Men and the New Teen Titans by Chris Claremont (writer), Walt Simonson (penciler), Terry Austin (inker), and Tom Orzechowski
This DC/Marvel single-issue crossover event is not classic, more of a rarity: the one and only time that these two teams crossed paths. The story is pretty standard fare for the era it was created in.
Visually it is still very appealing. One striking thing about the art is how Terry Austin's inks wax and wane. At times it is very apparent he is inking and the panels look much more like something out of the pages of his run with John Byrne on Uncanny X-Men; in other places Walt Simonson's distinctive style comes through much more clearly.
Walt Simonson spoke about this book on Comic Geek Speak Episode 814: Meet the Simonsons. An audience member asked him about the crossover event around the 40:45 mark and Walt's response lasted about 8 minutes.
For a plot summary and more information visit the Wikipedia page devoted to The Uncanny X-Men and New Teen Titans.