AutoDock is a suite of automated docking tools. It is designed to predict how small molecules, such as substrates or drug candidates, bind to a receptor of known 3D structure.
AutoDock4 and Autodock Vina are different programs. Both the scoring function and the search algorithm are dissimilar. AutoDock4 (4.2.6) is generally used for binding mode prediction and Vina for virtual screening. Vina is faster and has somewhat easier input preparation.
AutoDock Vina is the best software but can be a bit tricky sometime, especially if you make mistakes while preparing the protein and ligand. Also if you are looking to dock modelled structure then, the process is bit different than what you use while docking with a structure from PDB