For me , I choose bitcoin. There are so many sites in the web that has a great long term investments especially in bitcoins. Some sites for investing are legit's but also some sites are fake and not paying out. Watch out for that fake sites because all of your effort and money will be wasted in investing for fake sites. But investing is a very good idea even though is requires a very long period of time to claim but its worth it.
BTC will always be the top choice at any time in coming future. Its after btc that is what matters to me, since altcoin are currently very cheaply available if you compare with the btc so considering some good altcoin which can have a great future should be invested and bought now itself like XRP, Monerao etc.