All else being equal, the best fractional is rig is the one that is fractional enough to allow the benefits of the design (mast bending).. the higher it is, the bigger the headsail can be, and the higher the spin head is. But you lose leverage on the forestay to bend the rig. Fract boats started out at 3/4, then went to 7/8ths. For a long time now best is thought to be 9/10s for racy boats. We can bent the mast on BlueJ just fine, but we have a powerful backstay adjuster. You do see higher ratios for some models, most cruisers who are less likely to miss the the full range of trim adjustment.