Probably the most obvious choice for cryptocurrency holding, is by far bitcoin, but other than that the most sutiable altcoins for long term are Etheruem which is becoming more and more popular as its price is fairly stable and does not have a crazy chart, and the other would be ripple since there is a lot of hype to it, i don't really know here will ripple will go from now up until 2 years in advance but a lot of people have high hopes for it and i think that what makes it so popular and it would be a mistake not profit from this hype.