They both have prospects and basically for 2 different purposes, but asides so many things that makes bitcoin better, the fact that it has been able to stand the test of time, thrived no matter what and has a huge support Base, then I will always choose Bitcoin as No. 1.
It is true that ethereum and bitcoin have two different purposes in my opinion. Bitcoin itself has the most trust but is slower. While ethereum has so many different uses on contracts and so forth. I personally do not see ethereum taking over bitcoin any time soon or ever. The same thing that people like about ethereum is the thing companies don't like to many " this and thats".