I prefer to hold some alts, i will not sell all my alts because i believe that there are good alts that have a better future and there is a great possibility that it will follow the BTC's successful journey.
I agree the good part in alts is that they could easily x10 your money in just short period of time however it has more risk compare to bitcoin since this kind of coins could be easily manipulated , be very careful and smart when investing on altcoin there was a lot of money in there I assure you