The objective of investing is to make a profit, and that will be done with which Coins have the potential for a faster, higher price increase. BITCOIN is of course good and there is no doubt about it, but the price of BITCOIN is quite expensive, while ALTCOIN if we find a good ALTCOIN, can even get a bigger profit due to a higher increase and a cheaper Initial price.
An example is YFI from the initial price until now, the increase is quite fantastic. So which one will I choose between BITCOIN or ALTCOIN? My answer is that I will choose both of them provided that the ALTCOIN I choose is a very good ALTCOIN.