Those popular coin which is bitcoin and ethereum is good to invest because they have a potential to increase in the future so lot of traders waiting for it. But i suggest bitcoin because bitcoin is the most unpredictable of all coins that have a big pump.
Yes you are right and if I were the OP I will invest both in ETH and BTC. ETH has proven its volatility last year to which it even surpasses bitcoin in terms of market price volatility. However, we know that in ATH period BTC has more volatility than any other crypto in the market. So, it would be good to have invested both ETH and BTC.