Why do so many traditions and religions have saint men who claim having attained enlightenment? According to the suttas, the then Bodhisatta Gotama discovered by himself that ascetic practices of his contemporary India were not enough (or were even wrong) to attain complete enlightenment. Then, after trying his own methods and intuitions, he reached Nibbana.

However, many so-called saint men from other religions and traditions are said to have reached enlightenment in their own terms and according to their own definitions of enlightenment. We even have people within Buddhism itself claiming to have awaken, but still showing signs of craving and unethical behavior.

Considering what I've written, why should we deposit our trust, time and effort in the Buddhadhamma, when there are so many other practioners assuring that they have reached their ultimate goals following their own practices?

The most common argument for following the teachings of the Buddha is that when put in practice by ourselves we'll see how effective and accurate the teachings, analyses and practices actually are. But the same can be said about most other religions. 
We have a lot of examples of men and women through history telling stories and personal experiences of feeling the supreme love of god, or attaining Moksha, or becoming one with the Universe, and so on.

Can you help me to find new perspectives to solve this problem?

Thanks for your time!
The Buddha's teaching are unique in certain respects but their essential message is found in teachings from all over the world throughout history. The reason why so many claim enlightenment is that it is and always has been available to those who seek it. Were it otherwise the Buddha could not have become a buddha. There have been countless buddhas. 

So there is no problem raise by the many people who have claimed or been assigned enlightenment and wisdom. One would not need to be a Buddhist. It seems that the Buddha delved deeper and wider than most and there is no doubt he was a unique teacher, but we find the same essential message hidden in the Philokalia, the Corpus Hermeticum, the Upanishads, the Tao Teh Ching, the teachings of Al-Halaj and Rumi, the Kabbalah and elsewhere, the same claims of transcendence, no-self, formlessness and so forth. 

Beautiful Painted Arrow, a shaman of the Pueblo Indians, writes that in his tradition there are two states of consciousness available to human beings. In translation these are 'Believing we exist' and 'Awakened awareness'. Those who attain the latter state would claim some form of enlightenment regardless of whether they have heard of Buddhism. Truth is universal and the facts are the same for everybody.  

Enlightened beings are not uncommon but the Buddha is usually considered to trump most of them for his depth of understanding, knowledge and communication skills. If there were no claims of enlightenment from anyone but the Buddha then his teachings would be implausible and contradictory. He teaches that enlightenment is our birthright.  

It is up to each of us as students to assess the claims of all these teachers and 'saints' and examining the level of agreement between them would be a good indication of their knowledge. The diversity of these 'saints', once we have sorted the wheat from the chaff, is not a problem but a proof of the Dhamma. The Buddha was not a Buddhist when he attained his complete enlightenment.      

EDIT: The story as I have heard it is that while with his father he was instructed by Brahmins. Later, from Arada Kalama, who had three hundred disciples, he learned how to discipline his mind to enter the sphere of nothingness. Though Arada Kalama asked him to remain and teach as an equal, he recognized that this was not liberation and left. Next he learned how to enter the concentration of mind which is neither consciousness nor unconsciousness from Udraka Ramaputra. But neither was this liberation and he left his second teacher.