Why are there many Buddhist traditions?
The Buddha gave a wide variety of teachings because sentient beings (any being with mind who is not a Buddha, including those in other realms of existence) have different dispositions, inclinations and interests. The Buddha never expected us all to fit into the same mould. Thus, he gave many teachings and described various ways of practicing so each of us could find something that suits our level of mind and our personality.
With skill and compassion in guiding others, the Buddha turned the wheel of Dharma three times, each time setting forth a slightly different philosophical system in order to suit the various dispositions of sentient beings. The essence of all the teachings is the same: the wish definitely to emerge from the cycle of constantly recurring problems (samsara), compassion for others and the wisdom realizing selflessness.
Not everyone likes the same kind of food. When a huge buffet is spread before us, we choose the dishes that we like. There is no obligation to like everything. Although we may have a taste for sweets, that does not mean that the salty dishes are not good and should be thrown away!
Similarly, we may prefer a certain approach to the teachings: Theravada, Pure Land, Zen, Vajrayana, and so on. We are free to choose the approach that suits us best and with which we feel the most comfortable. Yet we still maintain an open mind and respect for other traditions. As our mind develops, we may come to understand elements in other traditions that we failed to comprehend previously.
In short, whatever is useful and helps us live a better life, we practice, and whatever we do not yet understand, we leave aside without rejecting it.
While we may find one particular tradition best suited for our personality, do not identify with it in a concrete way: "I am a Mahayanist, you are a Theravadin," or "I am a Buddhist, you are a Christian." It is important to remember that we are all human beings seeking happiness and wanting to realize the truth, and we each must find a method suitable for our disposition.
However, keeping an open mind to different approaches does not mean to mix everything together at random, making our practice like chop suey.
Do not mix meditation techniques from different traditions together in one meditation session. In one session, it is better to do one technique. If we take a little of this technique and a little from that, and without understanding either one very well mix them together, we may end up confused.
However, a teaching emphasized in one tradition may enrich our understanding and practice of another.
Also, it is advisable to do the same meditations daily. If we do breathing meditation one day, chanting the Buddha's name the next, and analytical meditation the third, we will not make progress in any of them for there is no continuity in the practice.http://www.fpmt.org/faq/buddhism_faq.asp#bteach