I started investing in crypto currencies two months ago. Firstly, before I invested, my idea was to only invest in BTC and ETH, but when I saw all the other low priced altcoins i thought wouldn't it be better to invest on those low price, which could go pretty easily x2 or x5 or even x10 in no time at all. So a good percentage of my portfolio was (and still is) altcoins, with which I'm now in loss. And I don't want to sell them now, the only thing that could save me at the end is to hold them for long term, because thankfully I invested in projects that could have a really bright future and could easily get mass adopted.
So let's say with altcoins, short term I didn't gain much, but the rest of portfolio that stayed in BTC and ETH and in pretty big plus.
My advice, invest only in altcoins that have great team and project and that you think might have great future, but let that be no more then 50% of your portfolio.