My personal opinion is the QuadX8 (octaquad) is probably the best - a good balance between thrust, efficiency and redundancy. You can use big props for the frame size unlike an X6 or X8 where the prop size is limited in order to fit them all in together. But one of the telling things is the number of commercial heavy lift multirotors out there using this configuration.
I was convinced by some comments from Tridge, amongst other things:
… and I think somewhere else he mentioned that they had a motor or ESC failure during testing and didnt even notice until after landing.
To be fair it could be argued that 6 or 8 motors in a more conventional format (see the google/Wing delivery planes) would offer similar redundancy, but then you are back to using much smaller props.