Ethereum and Bitcoin both are really good investment options but when it comes to market dominance, bitcoin beats ethereum by a lot of margin.
If I were to invest in any one of them I would invest in Ethereum because it has a lot of room to grow.
Not saying that bitcoin is a bad investment but if we compare the both, then ether would rise faster in price than bitcoin and provide better returns.
The best thing here would be to diversify in like 60% - 40% in both ether and bitcoin respectively.
Now is a good time to buy these coins as we are in a really good dip.
We might see a pump in price by the end of this year but that is just a pure speculation.
I have to say there isn't really a "big margin" because at the end of the day we are at just 2.5 or so higher in total market cap. I am not saying that it is not a good margin but to say that there is a big margin would be disingenious because it is not that much.
We know that etheruem is not catching up to bitcoin at anytime, so the difference between them will not be closed too much so why think that ethereum will go up too much compared to bitcoin? I believe that we should be focusing on either bitcoin/ethereum together, or if you want higher returns then you should be focusing on something that is a lot smaller, not just ethereum, but something like top 30 or so or even lower, because they have a lot more room to grow. I personally do not go towards anything lower all that much, I just end up with the top coins because I rather take less risk, crypto is already risky enough.
The margin thing is big according to me because I am looking at it from the amount of money required to match the margin of bitcoin.
Ethereum would need almost $375 billion more to match the market cap of bitcoin and that is some huge amount of money.
If we look at it from your perspective then yes 2.5 times would definitely seem like a small number.
Talking about the amount of growth, we are comparing bitcoin and ethereum here which is why I didn't talk about any other altcoin.
Ofcourse as you said, there are other coins which do have more room to grow.
I would personally diversify my portfolio with less risky coins and a little decent risky coins
(except for the fact that all coins are risky)