“The best exchange” already sounds utopian. Everything is quite simple. Some services are reliable, others are not. The perfect one should probably be convenient as CEX and sophisticated as Poloniex. But as you're new here, it would be better for you to start from something simple. On CEX, it's possible to buy btc or other coins with fiats using your cards or via bank transfers: https://cex.io/wires-campaign/.