Who is the most feared vampire hunter?

It depends on which literature one looks at. In the Classic Vampire Mythos the most feared Vampire Hunter would clearly be Abraham Van Helsing, after all he was the first real Vampire Hunter. Others to consider are Gabriel Van Helsing (no relation), Alucard (From the Helsing Manga), Blade (from the Marvel 'Verse), and Rayne from the BloodRayne series.