I wonder that, among the oldest languages spoken today, which one is the best preserved resembling its oldest known form in terms of grammar and vocabulary. I know that we are limited in our knowledge about the language history before writing is invented so an answer starting with written languages is good enough too.
What fascinates me is a simple word like "selam" (or "shalom") used in greetings actually comes from Sumerians thousands of years ago. I wonder if there is a language which preserves its oldest known form at broader scale from thousands of years ago.