I think one of the best altcoin that I have now is PRIV this project about security and privacy. PRIV now is gaining more supporters and the price of this is gaining too. But I can't say that I will not sell it because I need to sell it to buy more when it goes down and sell it again when the price goes up. And you can't hold altcoin forever you should know how to let go. 
I'm also watching closely and investing in PRiVCY, it's got a very active team behind it and a rapidly growing community, I personally think it will be one of this years major success stories.
There's not that many Airdrops that I think are worth participating in but PRiVCY is definitely an exception.