Takens and Dreads in my opinion is the most annoying enemy faction to fight.
------------------------TAKEN---------------------
THRALLS: Constant zigzag teleport, annoying to hit so your best option most of the time is just to wait for them to teleport up to you.
PSIONS: Duplicates even after they died. Just a waste of time and annoying, even more so on higher difficulties.
WIZARDS: Just like their Hive counterpart, they will shoot like a thousand slow moving shots a second that if you are close to them is an insta kill.
PHALANX: They use the worst game mechanic ever made, Knockback. They will rush up to you just to knock you away from them. Real fun and because Bungie knows how to program, their attacks like other, can go straight through objects and hit you.
HOBGOBLIN: Punishes you for shooting it by shooting tracking blast shots. Worse is the Overload version. Every hit causes them to shot you with Retaliation swarm shots. Tedious and sometimes near impossible to stun.
KNIGHTS: Insanely overpowered fire attack. Seriously their fire attack can kill you in a millisecond. It takes up a big area and last for awhile.
OGRE: Every single shot is a knockback attack. It is very easy to get pinned up against the wall or launched out of the map.
Not to mention their other uniques. Taken goo on the grounds that deals damage over time,
Blight domes that damage over time is often bugged and will kill you nearly instantly.
Then of course the Taken rifts that shoots blights that can deal infinite damage.
--------------------------------------------------------------------------------------------------------------------------------------
---------------------DREAD---------------------
GRIMS: Not really much to say here, flying enemies are not the most favorable ones. Tracking shots, dashing and Suppression attacks.
TORMENTORS: Strong tracking shots, a turret that most won't know you can destroy and of course the constant Suppression attack.
Weaver and Attendants PSIONS: Constantly flinging you across the map or freezing you.
HUSK: On death they will spawn a tracking missile that deals insane damage.
Strand and Stasis SUBJUGATOR: Suspension and insane base attacks. Slow and insane Shatter damage, That is when he wants to shatter it that is. Kind of random.
-----------------------------------------------------------------------------------------------------------------------------------
These are in my opinion 2 of the most annoying enemies in the game. Luckily there isn't that many Dread type enemies, but it wouldn't surprise me if Bungie added more.