Rushmore his best
I'm surprised he has never starred in a better movie since Rushmore.
shareI prefer Grand Budapest Hotel, although Schwartzman isn't exactly the main reason (Fiennes, Revolori, and Dafoe would all be higher on the success of that film). But Schwartsman was pretty key to The Darjeeling Limited, and while this might be a minority opinion, I happen to prefer that film to Rushmore. It's one of Wes Anderson's best.
Now, if you're just talking purely performance, that's a bit different, too, because he might have turned in a brilliant performance in a subpar movie. I'd still say he shines more in Darjeeling than at Rushmore.