It is better to have both coins because BTC usually has different trend comparing with other altcoins - during BTC Pump we usually see altcoins dump and vice versa...
Obviously it is better to have both the coins... but the question here is which one of them is the better coin... For me, it is a tough call. I first invested in Bitcoin almost six years back and BTC made my financial situation much better. My heart is still with BTC. But at the same time, I can't deny the fact that ETH is having huge future potential.