
I just completed Icebind run. - Don't pick Mobile Defense. Pick Disruption instead.
Disruption was by far the most ideal and comfortable mission type out of all the options. Every time you complete two conduits, the optional objective spawns at the location where the Demolisher was killed, allowing you to complete it quickly without risking mission failure.
Mobile defense, on the other hand, was by far the worst experience. You have to defend three terminals, and since the optional objective only spawns after activating a terminal, completing all three optional objectives requires all six players to abandon the final defense objective. This makes the mission extremely likely to fail, while the constant Defense → Objective → Defense → Objective → Defense → Objective cycle wastes a huge amount of time.
Personally, I really don't recommend mobile defense.