John S. Strong, in The Experience of Buddhism, refers to Nikaya Buddhism as Mainstream Buddhism (88-89), and differentiates it from Mahayana Buddhism. While there are clear differences between the two approaches to the truth, they do share basic elements, such as the belief in karma and nirvana, and the central place of the Buddha as an example of how best to reach enlightenment and liberation from the suffering and illusion of the self and the world. Both approaches to some extent advocate a Middle Way," with the Mahayana against both "self-indulgence" and "self-mortification" and the Nikaya calling for "the path between the extremes of eternalism and nihilism" (144). When one gets into the details of these shared beliefs, however, there are a number of clear differences between the two approaches, as there are in the different approaches of Christianity. Nikaya is the school which is more strict or conservative. Nikaya goes by the laws, the teachings of the Buddha, and stresses individual enlightenment of the special man, the monk, while Mahayana goes by the life of the Buddha, especially his compassion and service, and his decision to turn back from Nirvana to help others attain it as well, and can be said to take a more liberal approach. Nikaya sees enlightenment as a liberation attainable only by the few who follow the disciplines and precepts and teachings of the Buddhist canon to the letter. Mahayana sees enlightenment as being far more accessible to many more through compassion, rather than simply following rules and precepts and teachings. This difference affects how each approach views karma, nirvana, bodhisattva, anatman/sunyata, duhkha, Arhats, and pretas (hungry ghosts).
My own preference is Mahayana, because I would like to think that as many people as possible could reach enlightenment, and that it is not the exclusive club of those few who are able or inclined to live so strictly according to the teachings. It wou...