I think you should invest both. Bitcoin investment is more stable but profit is not as great as Etherum because Etherum is much cheaper than Bitcoin, which makes Etherum easier to price than bitcoin. But investing in bitcoins is still a very safe channel.
I agree with you, but in the present condition the bitcoin price is very high in the market and also it is the unpredictable job. Whereas ETH price is increasing in the market in a different way because there is no sudden growth in ETH but whereas BTC price is increasing very fastly.