Litvin’s Be Prepared for the AP Computer Science Exam in Java and Barron’s are both great, and have great explanations (though I think there were a couple mistakes in the Barron’s book). I can’t speak to the National AP Scholar award, but I don’t think that colleges will frown upon you not taking the exam after an AP course. Taking an AP course affects your resume positively. Scoring well on an AP exam affects your resume positively. Doing both affects your resume positively.
As far as resources, feel free to check out my Java guide, and feel free to email me with any questions.