In the 1 year bitcoin dominance went from 80% to 40%, so i think other currencies will continue to eat at BTC's marketcap.
BUT, BTC has 400 developer currently working on it and i think it will probably be the leader as they improve its functionality and build out the network.
You definitely cant ignore the other currencies at this point.
I like to hold many different cryptos and then adjust my holdings monthly as changes happen in the market.