The two of them also have a very big difference in the marketcap! bitcoin is 6x higher than what Ethereum has which imo cant even be called a competition. IMO, its not that its on a competition, both of it is like husband and wife in the market lol. Bitcoin has a lower coin supply and is more liquid than Ethereum but I can say Ethereum has its better technology which even BTC does use.
Nice comparison to husband and wife
I also think that at this point Bitcoin and Ethereum still have an independent piece of the cake. However, this situation may change over time .. And there will be a divorce 
I think it all depends on which of the partners will solve the problem of high fees faster.
