What is your favorite theory?

My favorite theory, not that i have a whole list of them in my head, is that it doesn't really matter where we go after we die- why not be the best human being you can be while you are still breathing and alive?  I don't understand people or religions that dwell so much on the rewards of the afterlife if one lives a noble life or one according to some rules written on a slab of stone 3000 years ago.  Sure, there was a time when I wondered about what happens to us and where we go after our heart has beaten its last thump, but I quickly realized I was wasting too much time pondering "what if" theories instead of just taking stock of what major religions and philosophies had to say about how to govern our own day-to-day lives. 

You make the best out of any situation, even though I still have some trouble remembering that; I'm realizing I have a tendancy of actually wanting to whine or complain or blame, and that doesn't accomplish anything.  I used to be so resentful (and truthfully still do get thay way at times) towards rich people or those from loving families.  I looked at them and thought, "Of course they're doing well in life!  Look at what they have or started out with!  How can they go wrong with such a strong, positive, financially-secure foundation???"  I think I just liked comparing myself to others, even if it made me feel weak or strong. 

I would agree with the age-old saying that we are all put on this earth for some reason; I guess i'm still trying to figure out how I want to leave my mark on the world and history.