Having your own car is the easiest way to get between wineries in the Hunter Valley, but it creates the obvious problem of drinking and driving. The practical solutions are: nominate a designated driver, book a guided tour that includes transport, hire a bicycle for the Pokolbin cluster (wineries are close enough together that cycling is feasible), or use one of the local taxi and shuttle services that operate between cellar doors.
Cycling tours are well established in the valley, with hire bikes available in Pokolbin. The terrain around Pokolbin is gently undulating rather than steep, and the distances between wineries in the core area are small enough to make cycling realistic for a half-day outing. For the more spread-out northern reaches of the valley, a car is needed.