Bitcoin is a safe investment. But buying some Altcoins too is a good idea. I suggest buying a bit of both coins. Both Altcoins go up and down, so if you have both you have a win win situation if you invest carefully.
I don't have enough money to invest in bitcoin just in altcoins since I can have capital from the campaign I joined to make an investment in it. It should be better to have both investment at a time because both are having pumps and dumps to take risk. To have a secure investment, taking the two will give opportunity to not lose any amount when investing.