Which two Yasawa Islands in Fiji for a 7 day trip?

I'm going to Fiji in July for 7 days with my boyfriend. We are in our mid-20s and will be flying in from Nadi and leaving from there too. As we're only in Fiji for 7 days and we don't want to constantly be travelling, I'm thinking that we could do one or two islands. If you had to recommend one or two islands that we must go to, what would you suggest? Thank you!