Landaa Giravaaru generally considered the better, but also requires a seaplane transfer.

Kuda Huraa is easier access, speedboat, and all that comes with it - including generally considered the more suited towards families. Having said that, though, they have recently done a big refurbish and added beautiful new infinity pools in many of the villas.

There's also (correct me if wrong) the option of staying at one, then transfering to the other via their yacht (Soneva does this too).