Pendjari National Park in Benin is the most developed of the three parks.
Pendjari covers about 2750 km2 of lightly wooded savanna, with 400 km of pistes. Several marked driving loops are in the area of the Campement de la Pendjari. Overall the roads are less bone-jarring and better marked than those in W and Arly.
The park was created in 1961 and added to the UNESCO World Biosphere Reserve list in 1986.
The park is officially open all year, but during the rainy season access is from Batia only, not through Arly. Heavy rains make the roads impassable. Wildlife viewing is often better in late winter (February-March) than earlier, as the animals are more concentrated at water spots. On the other hand, the temperature is pleasanter in December and January.
Walking in the park on your own is forbidden; you need a vehicle, preferably a 4x4. However, when you park at a viewing area (mirador) you can walk around that area. Try to spend at least 2 full days and a night, better yet 3 days and 2 nights.
The only lodging available within the park is the Hotel de la Pendjari, which is closed during the rainy season.
Benin: the Bradt travel guide. Guilford, CT: Globe Pequot Press ; Chalfont St. Peter, Bucks, England: Bradt Travel Guides, updated every few years..
Pendjari web site: http://www.pendjari.net/english/has a lot of useful information on practical matters. Also includes downloadable bird list and animal photos.