The best alts to invest in for a long term investment are Ethereum, Litecoin. These coins have shown great stability during this dip.
Ethereum being the second most popular crypto can be used as a platform for posting new ICOs. Also, its idea of smart and ledger contracts which can hold state and arbitrary code is great.
Litecoin since adoption by Coinbase, has shown great development in its market capital and has the potential to cross the $400 mark by the end of 2018. These are great coins and you can expect good profit returns from them.