The price of bitcoin is falling now so even altcoins in the coinmarket are affected by the fall in the price of bitcoin so for me this is the time to buy altcoins with potential and longterm I am sorry for your statement but if you buy bitcoin and altcoins now and leave it for 3 years I'm sure you will make a big profit.
With Bitcoin yes as it's been test by time, while with Alts not sure unless you sort it up.
Investing with project with solid foundation which in the long run ill bring you pure development and real usages,
from that event you'll find yourself harvesting the profits that those coins will give you 3 years is long enough to see
which project aside from Bitcoin that will flourished and gained huge benefits.