Hold bitcoin is more safely and proven profitable. After 5 months I bought 3 btc, I was got profit more than 30%. Before close this year, I will buying 2 bitcoin again and hold again.
Bitcoin has stood the test of time and it will stay strong in the coming years as well. I would recommend everyone to buy and stay invested in bitcoins. if you want to add other Altcoins, then invest 10 to 20 % of your bitcoin savings into Altcoins.
So investing for a long time can be still good idea in bitcoin but always check the news about bitcoin so that you can sell bitcoins if there is indication of danger mention in the news.