Ethereum, Litecoins and monero are the coins that has proven over time that they are reliable to invest in. There are next to bitcoins.
I am not sure altcoins can be replace bitcoin. Bitcoin is a huge cryptocurrency and the king all a cryptocurrency
do not think that of altcoins can be the next bitcoin
They are not supposed to replace bitcoin...
Bitcoin is just THE cryptocurrency, whose only use is to store value similarly to gold.
Now, the initial purpose of bitcoin, a fast decentralized way to send money, is fulfilled much better by other coins (LTC, DASH).
Essentially every coin is technologically better than bitcoin, but they aren't bitcoin...
So for long term investment, if that is all you want, bitcoin is probably still the bet decision.
Just remember that due to its essentially useless nature, it is always possible it may just crash.