Whenever I have Nasi Padang with my parents, we will each order different dishes, so there's an opportunity to try a wider variety. That's how I confirm which ones I need to order in the future.
From the Sinar Pagi stall at Geylang Serai Market, the standouts for me would be the "paru" (they cook the lungs softer than many other places), beef rendang (the meat is very tender and the "rempah", extremely aromatic) and the "sotong hitam" (the inky black gravy is rich and fragrant).