Bitcoin is stands out by its simplicity, security, and the fact that it was the first decentralized digital currency. It boasts a huge network and hash rate, which makes it very secure. While altcoins are aims to claim better scalability and innovation of Bitcoin, which lead to faster transaction and lower fees. I still believe, up until now Bitcoin is the best virtual store of value due to its wide adoption, altcoins often use advanced features but are more volatile and less secure because they react to vulnerabilities much more slowly. It all depends on the trade off between proven reliability with Bitcoin and innovative yet riskier altcoins. All that being said, I have seen Bitcoin has been quite innovative in recent years, I doubt that Altcoins can keep up, if Bitcoin keep being innovative and making break through.