My vote would be similar to what is used on aircraft and shipboard systems--400 Hz 3 phase.
Primary advantages:
Smaller, lighter transformers/motors.
No visible flicker from fluorescent lighting.
Higher ripple frequency means smaller, lower cost filtering components (chokes and capacitors) in AC/DC power supplies.
The above mentioned cardiac fibrilation issue.
3 phase power available to residences would allow the use of lower cost motors for things like furnace blowers and well pumps, as well as doing away with failure-prone start/run capacitors and centrifugal switches. Also makes for easy reversal of rotation.
The standard US 3 phase voltage of 208Y/120 seems fine to me, but the plugs/receptacles would have to change. The German Schuko would be a good starting point. I also like the British "fuse in the attachment plug" idea for appliance protection.
A GFCI main breaker set at around 100 mA would provide primary protection against "bolted" ground faults, with 20-30 mA units (in the breaker panel) handling individual branch circuits as needed for personnel protection. Individual single-phase branch circuits protected at 10, 20, or 30 amperes for lighting, general receptacles, or special purpose receptacles. Circuits for large appliances (ranges, A/C, etc. would be 3 phase.
Breaker panels would have a combination of gas tube and MOV surge protection right at the service entrance, where it can do some good.
