It has to be the Omnissiah for the fact that every thing is done with technology. The emperor would still be fighting off Tyranids with a pointy stick
Come now, we know what rests beneath Mars. The Emperor beat the Dragon with a pointy stick. Now the Outsider on the other hand.
"God-Emperor? Calling him a god was how all this mess started" - Bjorn the fel-handed, Venerable Dreadnought of the Vlka Fenryka. Imperial Truth trumps Imperial Creed. One was put forth by the Emperor...the other wasn't.
The Emperor specifically told everyone NOT to worship Gods and to do away with religion. If he ever wakes up When he wakes up his fury will know no bounds. Worshiping the Emperor as a God is going against His will, despite what the Imperial Creed would have you believe.
Yea just no one really knows it since he doesn't really contact anyone (that let anyone else know they're in contact with the Emperor.) Would be interesting to see how he reacts if he did get out.