I would prefer both but i will give many value to bitcoin, because there are a lots of altcoins that born every month. And their price will raise or go down in one-day. It's so difficult to choose a potential altcoin. Hold bitcoin it is more save.
I think you should consider your investment depends on what factors such as capital, profit direction, time to achieve profit, how to invest. If you start with a capital that is not too large, and there is a need to multiply that number several times in the short term, my advice is to invest in potential altcoin. Cheap Altcoin, low capitalization, often attracts investment and has the potential to grow in the future.