Many suits are scary, a heavy with a boundless, an amarr assault with a scrambler, a minmatar scout with knives. However all these pale in comparison to one suit.
The logistics. Why? Every suit mentioned above has their specific strengths and weaknesses. The logi however could be anything. He could be an assault trooper, or a remote det thrower, he could raise an army of zombies, or make any soldier twice as hard to kill. He can scan through walls and mark you for his zombies to see. He can lay down hives and uplinks so the fight is never far and the zombies are never out of ammo.

What I'm getting at is, logi suits are the most versatile in the game, they can preform so many roles you never know if two logis are the same. That scares me, As I know how to fight a suit with a specific role. However in a world where no two logis are the same you could kill one then be killed by a completely different set up.

Not saying this is bad, just saying out of all the suits in dust I fear a logi more than any other suit, because I fear the unknown factor. As a side discussion though, with the roomered logi Nerf would it be all that bad to slightly limit some of what they can do? Food for thought!

Maybe not to you, but there are two minjas that come to mind that scare me a lot, master kail and Mr mustard. I'll be honest when they are running around in their min proto scouts and knives in a city, I'm freaking out double checking all of my corners. They know what they are doing, where as a guy in a heavy suit or gallente scout running at my with knives is far less scary. Logistics that know what they are doing, scary, and I have to figure out what exactly it is they are doing!