I'm rather partial to LiFePO4 batteries at the moment. Super light, very high power density, massive peak energy outputs from basic batteries, and are quite safe.
A wounded LiPo battery will flare up like magnesium and at the least bulge like a balloon wrecking their mounts.
LiFePo4 won't do this.
Brushless DC motors and DC to 3Phase AC converters are amazingly efficient and cheap these days as well. Its a golden age for electric conversions. Everything electric is on the up and up.
http://www.abc.net.au/news/2015-07-11/a ... el/6612224