I went in Ruaha National Park more than 10 times in the last 6 years. I worked in Iringa region so Ruaha was the easiest park to visit during short holidays. In my opinion is one of the most exciting parks in whole East Africa. The main reasons to prefer the visit of Ruaha N.P. are:
Thanks to the low number of visitors (2.500 per year compared with Serengeti that hosts 250.000 visitors every year!) the experience in Ruaha N.P. is one of the wildest can be lived in Africa. Most of the game viewing occur in absolute isolation and solitude;
Ruaha N.P. is a typical river park, which means that all the park area is developed along a main river (Ruaha river). During the dry season the river is reduced to a small stream and represent the only source of water for hundreds of kilometers. All the wildlife must converge to the river so is very easy to see animals and very often predators can be observed during hunting. In this park the main prey for lions are buffaloes and secondary giraffes. All hunts are very breathtaking!
After the annexation of Usangu Swamp Ruaha N.P. became the biggest National Park in Africa, surpassing Serengeti and Kruger Park. Anyway, the main area useful for game viewing is relatively small and can be covered in one day.
All the tourist structures inside the park are hidden and well merged into nature. This helps to live a true immersion in African ecosystem. In every lodge and public huts (tourist bandas managed by Tanapa) the visitor is really inside nature and a direct interaction with wildlife is absolutely normal. Take care of your movements and follow suggestions and rules of park wardens.
I suggest to visit Ruaha N.P. from June to November (Dry season) to sight large game and predators. The rainy season (December-May) is very interesting for bird-watching and to see an explosion of colors and flowers. In rainy season usually – but is not a rule – is more difficult to see mammals.
In my opinion the two stars of Ruaha National Park are lions (the park is full of these predators) and kudus (easily sighted only here and in Selous), but all the traditional game are present. The only member of big five that you cannot see here is rhino, which can be viewed by tourists in Tanzania only in Ngorongoro.