Bitcoin seems to be the past and Ethereum the future.
The question is : when BTC will worth almost zero? Next year? In 2 years?

Bitcoin was still at the present in my point of view, then Ethereum for me was also a good investment too compare to other altcoins.
Ethereum could be always next into bitcoin but not in the sense that Eth can replace Bitcoin in the future. As far as I can see and I now every time Bitcoin goes up Eth will always be follows and when Bitcoin went down Eth will also do the same thing.