I normally use medium armor, and if I want to be extra fast I use light armor.
Don't get me wrong, I like the looks of chunkier armor, it is more my style.
But what is the use for heavy armor? I understand you are tougher to kill, but I am always left behind because it is slower.
Also I am still thrown around with explosions and I can't still be killed easily when overwhelmed, which I can avoid with medium or light armor by just healing constantly and running away.
So in what situations or what is the tactical advantage of heavy armor?
Stationary missions like termination or evac. Aside from that kind of mission I always run light armor. Heavy armor works very well on stationary missions because you're running around a lot less, so the slow speed downside doesn't matter as much.