To be considered a major Religion it should have answers to most of the questions pertaining to the individual(soul), world(universe), & God and the inter relationships therein.
If I'm right, Buddhism doesn't believe in existence of God (mentions only of mind). As does Jainism I believe (believes that the universe, souls have always existed, and no mention of God). Hinduism on the other hand (again in my opinion), explains most questions regarding all of the above. Incorporates what is called as Shad Darshanas where every person can take his choice or cult of worship if you like (cult of Shiva, Vishnu, or for that matter without having the need of a deity/image/idol i.e. meditate on the Supreme without form attributes). Hinduism is more open source structured. It also explains much better about the origins of the universe itself (claiming the universe is billions of years old and is cyclic, etc.). Well, to put it briefly Hinduism has already answered many of the fundamental questions about the science (like building blocks of matter - it clearly mentions energy which modern science is now finding out in String Theory). Some of the brilliant quantum mechanics physicists like Erwin Shroedinger read Vedanta (Upanishads) and he was able to comprehend his theories better. Philosopher Schopenhauer also read Vedanta and understood them deeply. These are just two who came to my mind.
In the past Hinduism was not only rituals etc. but a study of science itself. Its no accident that some of the profound scientific & mathematics have had their origins where the Rishis had the divine revealations. I would like to call them Spiritual Scientists. The latest discovery being the sixteen sutras for Vedic Mathematics which were recently rediscovered by Shri Bharati Krishna Teertaji while meditating in the forests near Shringeri. It is claimed that Buddha was able to tell the value of pi to several decimal places. Jaina saints were very advanced in their mathematics. The Rishis talked of mind bogglingly large numbers like 10 to power 54 and had different names for such large numbers. How? Meditation, divine revealations I would imagine.
My point is any religion which answers the fundamental questions of ouselves & universe is called scientific in nature. And science is knowledge. With knowledge ignorance is banished. Ultimately leading one (or mankind for that matter) to Peace.
In my opinion Hinduism is the most peaceful. That is why it is called Sanathana Dharma (eternal).