State your preference, and justify it. I could do with a laugh.
After thinking about the 'which is best?' question again and having all three main modes, F-hub, R-hub and a crank-drive, I can't answer the question easily.
All my bikes are legally compliant and each does a fine job though in slightly different ways. Conceptually, my favourite is the crank-drive with internal hub gears but the low-power motor in mine doesn't have enough oomph to get up hills easily.
The F-hub drive is the simplest of my bikes and is powerful enough for most scenarios though ultimately lacks the grunt available in the best motors.
The bike I enjoy most, I suppose, has to be the R-hub drive model which really feels like a crank-drive in practice with an excellent torque sensor and a powerful motor, capable of poodling along in too high a gear without complaint. Hills present no problem and 18 of the 24 gears are redundant for 90% of the terrain I ride over.
All that brings the matter down to the electrical parts involved rather the actual placement of the motor. By that I mean, if my rear-hub motor were of the same power output as the others I have, it would be difficult to pick a winner. Because it is more modern, more powerful and works in conjunction with a really good control system, it seems the best in practice but any comparison needs to take account of bike and user weight, motor output and gearing to draw any firm conclusion.
Just to complicate matters, we know that the same motor with different windings produces different power characteristics so regardless of the style preferred, once a legally-compliant motor stops contributing assistance, it's all about human power anyway.
Then, all other things being equal, the best bike is probably the lightest one!
Tom