Long Term: Bitcoins
Short Term: Altcoins
Bitcoins is the first cryptocurrency, and that makes it the most trusted and used amongst all the other altcoins, so its the most safe to get hold of. However, since the price is so high right now, don't expect it to increase tenfold in the next few years as it would be a little unrealistic, but possible though.
Altcoins, or Initial Coin Offerings (ICO), can have potential if researched upon, which makes it more profitable, however, there are many scamcoins revolving about ICOs and altcoins, making it more risky than having Bitcoin.
It is up to you, but if you are new to BTC, I suggest getting some Bitcoin first.

I agree with this. The most safest coin to invest is bitcoin because of its popularity and being the pioneer of all coins, it has been through many situations but still survive. ICOs short term investment is right though. There are some news stated that some ICO is just doing good for a month and later on little by little they escape. If you invest here in short term then it is just safer than other.