Sticky ends are most efficient in ligation because:
Sticky ends are produced when restriction enzymes cut asymmetrically within recognition sites, leaving short single-stranded overhangs. Ligation efficiency depends on transient association of fragments before phosphodiester bond sealing by DNA ligase. Cohesive termini can anneal through Watson-Crick hydrogen bonding between complementary bases, forming a stable, pre-aligned substrate that greatly increases effective local concentration of 5' phosphate and 3' hydroxyl groups. Blunt ends lack this stabilization and rely on random collision. Complementary pairing therefore lowers activation energy, improves fidelity and accelerates recombinant formation in cloning.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.