I think that for the following years, bitcoin will still be leading the market. The main advantage it currently has is that it was the first, the brand-recognition(People think of bitcoin when you say crypto-currencies), and that its the coin you use in order to enter the market of other coins.

Currently, some alt-coins definitely provide a advantage over using bitcoin(transaction time & fees), but if these do get improved with bitcoin, it will probably be leading for a long time.

If you believe that cryptos will be successful in the long term, you should probably try to invest in the top 5 coins, according to m.cap, adjusting every week or month, so that even if bitcoin is replaced by other projects, you will still end up gaining if cryptos are successful.