If coins i will suggest Lumens or what we called Stellar in past. Because that coin is very potential if i look. But this is only suggestion, not want to force you to bought it. Because for me, main coins is always good to pick, at least it is not tokens.
you want to find coins that you can buy with the exception of the 3 coins, you can buy TRON (TRX) or EOS, or you can search on coinmarketcap which is ranked in the top 10, so from there you can choose the most appropriate coin from you own.