[Child of the 7th Age]

There is a wholly different way to look at this problem, but I think it is one that sheds light and underlines the difficulty of trying to put a simple reading on a question like this. Somewhere in the Letters (I do not have the quote at my fingertips but I have personally read it several times), Tolkien explicitly states that each of the races of Middle-earth were intended to reflect different aspects of humanity: different characteristics that man possesses but which the author then represents in a more explicit or extreme fashion via a particular race.

In this sense, we are all Elves or Hobbits or Dwarves. For example, Man has the capacity to be a creator or to cling to his past and try to keep things from changing. He also has the ability to appreciate the smaller things of life: to enjoy being with family, relishing a good meal, or nurturing growing things. In that sense, not only do characters like Boromir or Aragorn reflect our human nature and destiny, but so too do Gimli and Sam and Elrond. Why else do we respond to the characters as we do? How often when we read about a supposedly non-human character do we instinctively feel that we know and understand that individual perhaps as well or even better than the other "human" characters in Lord of the Rings?

Certainly, the Hobbits and the Shire have always represented for me a great deal of what I realistically understand about human nature. With his struggle to grow beyond what he is, his innate loyalty coupled with a definite parochialism, Samwise has always seemed to embody many of the possibilities that lie in the soul of mankind. And I would say the same about Saruman. We certainly have too many Sarumans running around today, using their silver tongues to promise us things that simply aren't true and, driven by a desire to succeed, wholly disregard the needs of the earth.

In that sense it is wholly impossible to point to a "representative man" in Lord of the Rings, or to say which character best embodies the nature or fate of humanity. All of the characters exhibit characteristics, bad and good, that we possess within our own souls. Saruman and Sam have as much to teach us about who we are as those characters officially identified as "Men".

The closest I could come to answering your question is to point to the character with whom Tolkien identified most closely: that of Faramir. Again in the Letters, Tolkien states that it is Faramir who most nearly mirrors his own personality, his likes and dislikes. It was for this reason that he gave Faramir the dream about the drowning of Atlanta (aka Numenor), which both he and his own son Michael shared. And it is perhaps not surprising that the character of Faramir was never planned, but was one of those who came popping out of his head without premeditation.

In the end there can be no one character that embodies humanity. Each of them share a tiny piece of who we are and what could happen to us. We could populate our earth with Sarumans, Orcs, or even "fallen" Boromirs, or we could develop into Samwise or Aragorn: the choice is up to us.