Depends your country and state. I don't know. Coinbase is good for most Americans. I don't know much for everything. Swissborg is probably best for non-Americans but I am an American so don't know much about it.
Kraken or Binance would be the best but it's complicated and a long process to wire money to those.
The Bitcoin price is very odd right now, it can't decide if it will go down or up, but there's crazy high buying pressure now. There's also institutions who want to manipulate the price lower so they can buy more.
Again, if the price of Bitcoin goes into the $20K range I'm personally buying that. Wait a few days or a week before you do anything. That's what I'm doing.