Bitcoin is the main Crypto-Currency, the best one. Some people like to invest in ETH or diversify funds among different currencies, but I personally would prefer for now to put all my tickets in BTC. The price will probably increase a lot in few months (who knows, maybe 50%-100%), I'm not sure if ETH has the same potential... I don't think so.
1 BTC worth much more than 10 or even 100 ETH.
Especially because you want to put it into a cold wallet for at least 5 years, BTC potential is huge on long term.
bitcoin uses an outdated architecture, I buy it on a trend, in fact, its transactions are very expensive, there are many alternatives to bitcoin, the etherium is cheaper, faster and most importantly it creates many altcoys that are also successful.