I think the coins that on top are safe and reliable. They have survived for a long time in the market so they will not die easily. I just invest into the coins that in top 20 because I think they can give me enough profit while they are much more safety.
But that cannot be a good investment advice, i would say. You cant just invest in the Top 20 just because they are in the top.
a) Because the are in the top, means that most probably the price is already high.
b) And most important is that *first* you shall read the Whitepaper, or at least get more involved in the project, before investing on anything!