As a current LEAF owner and former i-MiEV lessor, I will tell you the LEAF is a much better vehicle.
Highway speed ride quality is about what is expected for a short-wheelbase car with very narrow tires. Crosswind stability, however, is terrible.
The i-MiEV is a great in-the-city vehicle or commuter vehicle. Don't expect the level of comfort the LEAF provides. That being said, the i-MiEV's rear-wheel drive, excellent visibility, and tiny turning radius make for an amusing driving experience.
At $4000, that car is a bargain. The batteries don't have the capacity loss issues the LEAF has.
2012 Mitsubishi i-MiEV ES (lease ended) • 2015 Nissan LEAF S • Tesla Model 3 reserved
Mods: Matte black Juke wheels, LED headlights and accessory lights, horn, CarPlay receiver