You'll get different answers for this question because it depends on the preference of each investors. Bitcoin and eth are the most trusted cryptocurrencies of investors for being well-established, existing for years and also dominates the market. That being said, whatever you choose (to be a much better investment) its fine because both are reliable to likely give us huge profit especially for long period hodling.

But as for me i'd rather allocate a portion of capital on each coin and will not switch to be on the one side only. Since they're performing well on the market, then I can take advantage the increase if I invest to both.