As always, it depends on the investment profile and willingness to risk. A balanced risk approach can be to put half of investment to btc and half to altcoins, of course after some research and analysis. Investment purely into btc would be of course safer, but unless a person invests a lot of money, it will not make him really rich. I would say that even the biggest optimists do not expect btc to grow 1000x in the near future, which is still possible in case of some altcoins.