When investing, Im a big fan of diversification of portfolios. I believe that both Ethereum and Bitcoin offer value, albeit in different ways.
Even though Ethereum is positioning itself to become a large platform, the fact that Bitcoin is so well known makes it the first place where people invest.
I think you should hold the bitcoins as it would be more valuable and profitable in the long run if we compare the same with Ethereum. You can invest extra money into the ETH but don't loose the bitcoins at this moment.