If you are just after EDC, Infected Space Elite is the easiest. No fail option.
Getting the Optional can even be done with an all cruiser team.
The way to go is:
Clear the trash mob.
Prep all 4 nanite generators for destruction, get them to around 10-15%.
Blow them all up at the same time.
Don't bother with engaging the spheres that will spawn. Focus all fire on the transformer which will go down faster then any nanite sphere can reach it to heal it.
Then it's a matter to focus on the newly arrived ships and clean up.
Then repeat the same procedure on the other side.
When the second transformer blows be carefull not to go anywhere near the tactical cube to avoid premature aggro.
When second sphere waves are gone attack the gate from the backside.
That just leaves the tac cube. If you had a smooth run so far you should at least have 5 minutes left.
The tac cube has a habit of one-shotting even the toughest ships.
Aggro managment is important here.
Keep an eye in who gets targeted. A dedicated Tank can take it's fire with some well timed resists and good gear.
Everyone else get out if range asap.
If you keep hanging outside it's weapons range while targeted everyone else is save.
As a tank I dive back in when my cooldowns are done to keep the aggro.
You will never completely avoid dying and there is a death penalty in Elite STFs.
You will accumulate injuries with each death that will reduce your effectivness severely. So bring a stock of repair components if each variity: minor, major and if you have some critical.
Use it right after dying while the respawn timer is still counting down to save time.