The best time to visit Botswana is in the autumn and winter months (April–September), the dry season; however, it's also the most expensive time. In the Delta during the winter months the water comes in from the Angolan highlands, and the floodplains, channels, lakes, and inland waterways are literally brimming with sparkling, fresh water. Elsewhere, because it's the dry season, the grass and vegetation are sparse, and it's much easier to see game, which often have no choice but to drink at available water holes or rivers. But be warned: it can be bitterly cold, particularly early in the morning and at night. Dress in layers, which you can discard or add to as the sun goes up or down.
During the green season (October–February), aptly named since it's when the bush is at its most lush and is populated with lots of baby animals, you'll find great economy deals offered by most of the lodges, but it can be very hot, especially in October and early November when temperatures can reach up to 35°C (95°F) or more. The rains tend to arrive from November onwards and can continue until late March or early April, which helps to cool things down but can impact on your activities. If you're a birder (Botswana has more than 400 species of birds), this is the best time to visit because all the migratory birds have returned; the green vegetation also provides an attractive backdrop for keen photographers. Generally speaking, though, unless you can stand great heat, don't mind getting wet, or are a devoted bird-watcher, stick with fall and winter.