[waterheater]

Tokamaks are conceptually elegant but contain significant inefficiencies which negatively impact potential net power output. Both tokamaks and optimized stellarators have magnetic fields possessing omnigeneity [1], but tokamaks require two magnetic fields (poloidal and toroidal) whereas stellarators employ one.

The bigger question is if magnetic confinement fusion will lead to the best energy producing devices. Competitors include inertial confinement, pinches, or some other exotic method. If a magnetic confinement fusion device produces net power, it's going to be a stellarator.

Sources:

[1] https://en.wikipedia.org/wiki/Omnigeneity