To start off, I'm not incredibly experienced with electronic modifications and what have you; but I'm going to give it a shot anyway.
Anyway, I think it depends on what you're looking for and how much time/effort/money you would be willing to put into the project.
Electric springers probably have a lower potential fire rate (when compared to that of flywheels), but greater potential ranges (with the right springs and gears). Flywheels on the other hand, are probably cheaper, faster, and easier to install.
Idk. Just an educated guess from the little experience I have.
Hopefully someone else will explain this better than I did.