It is always a good idea to diversify when you want to make an investment but at the same time you shouldn't force yourself to buy multiple things and invest in them just to have diversification.

What you buy should be a well thought investment.

So i say yes to bitcoin. as it is the best investment around.

As for altcoins i will only invest in Litecoin for a long term investment but the rest are only good temporarily and you should buy and sell them fast.