Why would I choose to use Bitcoin and not other crypto currencies like Ethereum or Dash? Why is Bitcoin better or worse than the rest? The title basically says it all, I'm a new investor looking to fill out my portfolio but I also want to know the lay for the market, what cryptos are worthwhile, and why?
I find this article convincing in its analysis of the dynamics between Bitcoin and competing networks: The Coming Demise of the Altcoins

To summarize briefly, the author suggests:


The utility provided by a currency system is related to the willingness of its users to save using that currency. 
Currencies have a strong network effect.
Most altcoins don't have a significant technological advantage over Bitcoin.
Therefore, altcoins are destined to lose value in comparison to Bitcoin in the long run.


I do recommend reading the article, though.