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.

Bitcoin is the best coin among other coins, so it is great to choose as an option to invest when you have enough capital .. You definitely want to make a profit in investing and bitcoin is the right choice ..