Bitcoin shows main trend and other alts keep around. Some of them could go high, some low. It is like a lottery or casino bet.
So if you want invest and not play casino you should buy bitcoins (But you must think with your own brain
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Wow, that's the worst analogy I've heard of altcoins. Lottery, Casinos and Altcoins? Very little in common.
If you want to invest in altcoins and you don't want to risk too much, invest in some of the top altcoins. NEM, RIPPLE, NEO, ETHEREUM...
Yes, you can invest in bitcoin, but the profit on BTC cannot compare to the one you could get on an altcoin.
BTC is growing, yes, but it's growing slow, in order for you to get 2x your investment, BTC needs to reach almost $8000, which is not easy, as it cannot break the $4000. There are not enough investors to keep it above $4000, so I think it will dip back to $3700.
If you go on an exchange, you can see altcoins increasing by triple digit % every day, that does not happen with BTC.