Ruin 1 and Ruin 2 can be used together or alternating according to when you have to move or when you have mana to burn.
Energy Drain is only and ONLY useful for getting mana back when you need it right away or when a bard is unavailable - like when you had to res 2 people in a boss encounter (Titan comes to mind) and run low on mana.

Fester is way way superior to Energy Drain and should be the majority of your Aetherflow usage.