What about cheapest fee platform to use?
It will depend on the payment method on various platform, you can try to buy your bitcoin at Binance it's 3.5% per transaction I think it has the lowest fee for buying bitcoin in a platform. It's better to buy bitcoin here than the most online platform.
Great recommendations mate, aside from binanace in my own experience Poloniex is one of the trusted platform you can buy bitcoin with lower transactin fee than to others.