Best baby formula??

Gemma • ❤️❤️❤️❤️
Soooo I have made the decision that I'm going to Breastfeed as much as possible but I know with expressing and feeding there are going to be times I physically can't Breastfeed. I was thinking about formulas to buy so I have one ready incase but I have nooooo idea what to go for? Anyone used any formulas before? And which did they find was best substitute for breast milk??