In Epic Wars, such things a turtles doesn't stand a chance, therefore you never trust your defence to proctect your fleet or ressources.
Still using defence, can be a very good idea, it will scare a lot of smaller players away from raiding your planet from ressources.
There is a lot of theories about "the best defence", but there is a few things most people can agree about.
Fodder is needed in every defence, this can be Rockerlaunchers, Light Lasers or Heavy Lasers - these defence units is quite cheap and is used in large numbers to draw the fire away from more heavy defence units, as Guasscannons, Ioncannons and Plasmacannons.
Guasscannons, Ioncannons and Plasmacannons stands behind lots and lots of fodder and fire opon the enemy, recieving few shots due to the random shoting most likely will hit the fodder.
A good defence could look like this:
20.000.000 Rocket Launchers 20.000.000 Light Lasers 10.000.000 Heavy Lasers 5.000.000 Gausscannons 3.000.000 Ioncannons 1.000.000 Plasmacannons
As mentioned earlier, the large amount of cheap defence prevents the heavy defene from getting incoming fire and make them stay alive long enough to fire more times, inflicting more damage.