They both have similar wireless properties (900MHz, devices are repeaters). Z-Wave may have a more robust RF software layer. Insteon adds powerline signaling so it could be a benefit. Don't forget that 2412N is powerline only and you might want to consider using either the new Hub (read reviews first) or another controller with the dual-band PLM.
Insteon will be more reliable as it's immune to wireless interference. Two things can affect remote signaling, wireless interference, and powerline interference (for instance, from improper grounding, or an old refrigerator). Since it's rare to have both at once, Insteon covers both angles, and can use either powerline or wireless interchangeably. Z-Wave may have a better software protocol, but for your use, you'd never notice the difference.