Students who have used Stewart or Larson often switch to Salas and Hille for the challenge. The problem sets are legendary. They don’t just ask you to "find the derivative"; they ask you to derive the derivative formula from first principles. The exercises are grouped into "A" (routine), "B" (moderate), and "C" (challenging theoretical) levels. The PDF format allows students to reprint problem sets and work them out on physical paper—a hybrid digital/analog workflow.
If you are a student or self-learner:
Salas, Hille, and Etgen offers a rigorous, classic treatment of calculus that prioritizes conceptual understanding and proof over rote memorization, making it a gold standard for students who want to truly understand why calculus works, rather than just how to solve problems. Salas And Hille 39-s Calculus Pdf