Most altcoins are completely junk I'll give you that.
There are however some altcoins that fill roles that bitcoin currently does not.
For example if you want a truly anonymous coin you'd need to have Monero.
If you think that decentralized assets will become a bit hit then either Counterparty, Etherum or Aetherum would be a few good choices.
If you think that SuperNET will succeed potentially having a small amount of bitcoindark would be a good investment.
Stay AWAY from Ripple centralized scamcoin and pretty much every other altcoin out there.
Bitcoin is 100% guaranteed to succeed in my opinion. After that I give
Monero a good shot due to its anonymity. Whether or not a small amount of counterparty and bitcoindark is worth it to you depends on how much you want to gamble/speculate.
Don't gamble any of your coins. Don't believe any investment site. Keep your coins on your own secure trezor/cold wallet etc. Come back in 5 years and profit