I would have to agree that Bitcoin is the best. It's by far the safest cryptocurrency and the market generally follows its movements. This doesn't mean you can't lose money, of course, but that means every other alternative is likely to lose more. Holding it can lose you money, but it can earn you money as well. It's guaranteed to grow as the crypto market grows. It's also the most liquid crypto, being accepted everywhere crypto is accepted.
You'll have to weigh the options on your own and find out where your priorities lie. For what it's worth, majority of holders choose to hold Bitcoin as their primary coin.
I heard about one fact. It's not good to keep in one currency. I think in the case of Bitcoin I can be calm. Its price will fluctuate. But it can't disappear altogether, are you agree?