Step 1: Rank the three malignancies by their 5-year survival, which is the standard surrogate for cure in pediatric oncology.
Step 2: Among these, retinoblastoma tops the list at roughly 97% survival. It is frequently picked up early through leukocoria and is highly curable with current treatment.
Step 3: Nephroblastoma (Wilms tumor) follows with about 88% survival, very good but a step below retinoblastoma. Rhabdomyosarcoma trails at near 61%, reflecting its more aggressive course and frequently later presentation.
Step 4: Since the figures clearly differ (97% > 88% > 61%), the choice All cannot be right, and the single best cure rate belongs to retinoblastoma.
\[\boxed{\text{Retinoblastoma}}\]