You probably won't notice a huge difference between any of them, although the Comptech and Fidanza are actually the two lighter units (and are also "USDM" and as such have never displayed the starter grinding that certain JDM units have when installed on US cars).

Toda proponents often bring up the valid point that overall weight isn't the only factor that affects how a flywheel "feels", and that the distribution of the flywheel's mass (i.e., centralized vs. towards the outer edges) plays an important part as well. That being said, while Toda touts that their unit is built with this weight-centralization in mind, to the best of my knowledge there hasn't been any testing or evidence to prove/disprove this claim, or to indicate that the other, lighter flywheels don't also have this "favorable" sort of distribution.

Of course, there is then the entirely different considerations of chromoly vs. aluminum, replaceable friction surfaces, etc.

I think it would be great to see some sort of flywheel test put together, where various offerings are weighed, and their rotational inertias are somehow evaluated.