I am sure that investing in altcoin still worth it in 2019, and we have so many potential coins at the market so we can choose more than 10 coins list. But the problem is we cannot always manage and watch the coin movement so we might get too late to see that coin increase later if we are not ready for the increasing of the price.
If that person will invest in only those coins which have a better future and the developers are very active for the project then buying them and holding for a long time will be a safe way to invest in these altcoins in this year as now the crypto market is on its best timing.