Not in winter - there's not much to look at, the vines are just a woody mass and it's normally cold and wet.
In spring the vines are coming alive again (April/May in the northern hemisphere). In July/August the vines look lush, the grapes will start to ripen, making it a great time to visit. However, the French and Italians are often at their holiday homes or on the beach in August so the wine regions can seem like a ghost town.
While harvest time might seem an exciting period to visit, the cellars are often too busy making the wine to receive visitors. Autumn is always a wonderful time to see the beautiful colours and catch the last warmth of the year.