Two ways to build a hybrid
Both systems use a petrol engine, two electric motor-generators, a small battery and a power control unit. The difference is how engine power reaches the wheels: Toyota splits it mechanically through a planetary gear, while Honda mostly turns it into electricity first.
Toyota: power split and e-CVT
The engine turns the planet carrier, and the planets split its torque between the sun gear (MG1) and the ring gear (wheels), so part of the power always reaches the wheels mechanically. Changing MG1's speed sets the engine's rpm with no gear shifts, which makes it a continuously variable transmission. MG1's electricity and the battery power MG2, which adds torque, drives the car alone at low speed and recovers energy when braking.
Honda: series hybrid drive
In Honda's e:HEV the engine only turns the generator motor, and its electricity flows through the PCU to a large traction motor that drives the wheels. With the engine off, the battery runs the motor alone (EV mode), and under hard acceleration the generator and battery feed it together.
Honda: lock-up clutch
At steady highway speeds, turning power into electricity and back costs efficiency. A clutch then connects the engine directly to the wheels through one fixed gear ratio, and the motors only help or charge as needed.
Toyota: pros and cons
Pros: there is always a mechanical path, so it is efficient across a wide range of speeds; it has no clutches or shifting gears, and decades of mass production have shown it is very reliable; it is compact and cheap to build. Cons: under hard acceleration the engine revs high and drones (the 'rubber-band' feel), MG2 is smaller so electric punch is modest, and at high speed some power circulates through MG1 and MG2, which wastes energy.
Honda: pros and cons
Pros: the big traction motor gives strong, instant and smooth torque with an EV-like, quiet feel, and because the engine is decoupled it can stay at its most efficient load. Cons: in series mode, turning power into electricity and back loses energy; the single fixed ratio only suits a narrow cruising band, so at high speed under load it falls back to series mode; and the larger motors add cost and weight. Real-world fuel economy ends up very close to Toyota's.
The winner: Toyota, narrowly
Overall, Toyota's power split wins by a small margin: it has the longest record for reliability, costs less to build, and stays efficient at every speed, including on the highway. Honda's e:HEV is the better choice if driving feel matters most, because it is smoother, quieter and more responsive. On fuel use the two are close to a tie.