Having etherium and bitcoin is much better. But if I have to choose between the two coins, ofcourse i will choose bitcoin because of the popularity and stability of it.
Both are good for keep and wait for more adoptions, though more are into Bitcoin since it's been adopted and known first.
Just look at the value of the bitcoin ten years ago compared as to date, it is getting high. Many people adapt bitcoin for their transactions, like paying ultility bills, grocery, buying clothes and others.
That's why the value is rising, adoptions and usages really affects the price, for sure more will see this advantage and start investing.
We also know the bitcoin is the highest valued coin compared to the others. I should go for bitcoin in terms of investment. Etherium also is stable, the value of it continuously increasing. Both are good coins.
You can split your money and hold both, looking for long term both projects are good for sure.