I got the cerulean nova, but is there really any difference between energy and kinetic damage, or is it just for flavor?
As damage types, no, there isn't any difference. For the relics that deliver the relevant damage types, there is. The Kinetic and Internal proc relics utilize your Tech crit chance while the Energy and Elemental relics utilize your Force crit chance. Since your primary attribute only contributes crit to your actual power source, your Tech/Force crit chance (whichever one isn't listed in your character sheet) is generally ~10% or more lower than your Force/Tech crit chance.
As such, since you're talking about a Rage Jugg, you should use an Energy proc relic. If you were a Gunnery Commando, you would want to use the Kinetic proc relic.