Why not both?
I agree make investments into bitcoin and ETH, it is good ideas becauseif one of both there is increasing the price will give profit or if they are both
increasing of price, it is mean will get maximal profit,
but always remember about the risk losing money in trading and must be calculated about it.
i think not just bitcoin and eth that we should make invest but we have to invest for the other coins that have a good chances to rise like before because when bitcoin price is down then i think its the time for altcoin to gets up and reach new price level and there should be many high price in short time before bitcoin price is getting up again. so i think i don't want to getting late to make invest from now.
you can see the title it is about bitcoin and ETH which are the best coins for investing for long time
and we don't talking about trading altcoins except bitcoin and ETH.
