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.
Exactly, you have explain very well, I do agree with you. Firstly, Bitcoin is best now and also forever, but better to invest in bitcoin for a long time, then it will be a profitable, and if we have big capital to invest then also bitcoin is best. But if anyone have little bit money then better to invest on altcoin and as you said altcoins are better for short time investment.