First not an altcoin but safest and the best investment and that is BITCOIN , sorry but you must add this everytime you invest in crypto .
Second is BINANCE as the most popular and best alternative coin ever created , from use and utility this is the best option .
Then of course ETHEREUM , being in the market for years and being second biggest coin for more than 5 years now? this will be the safe and manageable investment .
You mean he must buy btc every time he buys another crypto but what if btc is up and other cryptos are down, it would be wise if he skip btc first and pick up those dump coins first. Altcoin is not a single coin but when you say altcoin, it is already composed of different cryptos and there should be safe altcoins. Not all altcoins are scams.
Binance coin isn't the most popular altcoin but it was eth I guess because eth is older than it and eth is also the second biggest coin but no doubt that binance coin are a good alternative coin and can be better in some ways than eth. Ethereum can be a good coin but manageable ? not sure about that because the fees in eth are currently high.