I think some of the altcoins such as Monero, Litecoin, Ethereun have a lot of potential to grow.
Firstly the speed of transactions of Litecoins is four times faster than bitcoins which makes it more preferable.
Ethereum has one of the strongest development teams which will help it in faster growth.
Monero is the most preferable market coin other than bitcoin as it is completely anonymous and the transactions are secure and untraceable.