whats the best currency to invest?

BTC is always a safe bet in crypto. Almost all of the infrastructure is built around BTC. That being said, you will see less risk in BTC and therefore less gain. I personally like privacy coins and coins that could serve as a good store of value. For that reason I really like Beam. They have created a coin that is really fast, has a finite supply, and is in my opinion the best all around privacy coin at the moment. *This is subject to change without warning at any time. Crypto technology is always improving and others becoming obsolete. You really need to do a lot of research and then stay involved once you invest.