Which is the best bitcoin exchange with the lowest spreads and transaction fees?

Bitfinex has low spreads most of the time. Transaction fees are 0.2% but fiat withdrawals are quite expensive. So I’d recommend to do trading on Bitfinex and fiat withdrawals on kraken or bitstamp which support many different withdrawal methods (it’s especially cheap for SEPA payments).

Well, there are a lot of options actually. Still, I would recommend to explore theCryptocurrency Exchange https://www.crypto-rating.com/exchanges/ it provides a lot of professional information that will help you in your work. Depending on which product you choose, you can understand what the price is at the moment and whether it is worth investing there.