I feel like leg curls isolate them more. So, for effective HS development, I would go with them if it were the only Hammy exercise... But, I love SLD because they work your glutes and lower back as well.
Don't forget squats!
Do 'em all... Or, switch up each time you workout.
For complete development, you need both a hip extension movement like stiff-legged deadlifts and a knee flexion exercise like leg curls.
I like glute/ham raises, which hit both functions pretty well.Tough exercise.