Two words from your post "investment"and "safest" doesnt come together when talking about cryptocurrency.
I would try a bit different approach - I think NEO, Monero, LEO, CRO are the worst altcoins to buy in top20.
Neo - I dont here any positive news or about about it. The only way its price could go up is a short term pump.
LEO and CRO - just unknown alts. I think they dont belong to top20.
Monero - I've suddenly realizes, that the word scam is often used when speaking about Monero. An altcoin is not a scam by itself, but scammers often steal XMR tokens, XMR was used to scam or something like. I guess it is just a bad karma.