In regards to combos that seemingly every melee class gets, does anyone know the distinction between “brutal” and “regular?”
For instance, Brutal Enraging Strike vs Enraging Strike.
These seem to be essentially identical attacks. Are they meant to fill directional attacks that your more common combos don’t usually cover? Is one simply superior to the other? Should both be used? Only one? Neither?
What’s the deal?
nobody use them at lategame as far as i know, so don’t worry too much about them, one has more starting combo damage than the other, and the other has more ending combo damage than the first. (which is more important)
On lower levels you can use them whenever you need them (if the shield’s are aligned in a way that makes other combos “useless”), once you hit level 80 though, you shouldn’t use them anymore (or even before that, maybe max. Level 65 or so) because their damage is very low compared to other high rank class combo attacks. Additionally to having more overall damage, these high rank combos also have synergies with certain feat tree perks which the low level archetype combo attacks (every soldier class has the same and every rogue class has the same) do not have.
It honestly depends of your background roleplay. I prefer to roleplay my character as a mentally challenged barbarian who doesn’t really learn new ways to fight, so I use them until lvl 80.
Take the Soldiers Enraging Wound and Brutal Enraging wound -> they are pretty potent combos while leveling, they dont share a cooldown so you can use both and their combo starter starts on different sides. So while they both end with an upper arrow (or rather hit the front side/shields) one starts with a hit to left, the other with a hit to the right. This is important, because NPCs react with their shielding on your preferred directional attacks. Thus if you run thru the jungle and use the level 2 combo “Sweep” (that ends on the left side), most enemies will immediately put thier shields on that side, so that further combos to the left will be less effective. So while leveling - and later while tanking - you somewhat want to balance out your directional hits and finishers!
Let’s say you’re a Dark Templar. You could always alternate between 2 Versions of Blood for Aid and never use something else. But if you’d do that, the enemy will put all his shields to the right side (B4A ends right), and your physical component of the attack will deal less and less damage. Instead you want to add more combos to your rotation: 1st to benefit from the buffs/debuffs those combos provide (like Leech Life give you physical health leech) and 2nd you want to diversify your directions to control the enemies shielding, increasing your own damage, aggro and usually also increasing your teams damage*
For those ‘generic’ combos or Tortage combos like the enraging strike etc: while most of them become useless in late game for most classes under most circumstances, there are at least 2 exceptions: Slam and the Enraging wound that starts to the left (not sure if its the brutal or not) for the DT → Dt excells at proccing damage. ‘Procs’ mean, that your hits have a chance of dealing additional damage, just by hitting - independent of the combo used. A DT has tons of those procs: Blighted Touch, Covenant of Arms, Pact of Malacodor, Void of Madness etc. So at a certain point you dont only want to use the Combo that deals the most damage (like Blood for Aid) with its finisher but you also want to maximize the amount of hits in a certain time. And the enraging wound does have a lot of hits relative to its short animation time (Three hits in the finisher and no further following attacks after the starter). Also the DT doesn’t have many combos hitting the left side, so a combo starter on the Left is really useful. Same with Slam: no preparation at all, just 2 Hits in the finisher, which is really nice, when trying to build quick aggro on an Add so you can use irritate on a second add to position them properly, before the DPSers mess up the whole positioning 
*if your team has no deeper understanding of how to position and reposition themselves during fights to always hit unshielded sides - which most players dont have
Standing behind the boss to avoid all shields and happily doing massive amounts of damage and then suddenly the tank decides to turn the boss towards you for no reason at all and messing around with the shields, yeah that can be really annoying. Even more if you are completely blocked by spellweaving casters that don’t let you escape.
well, standing in the bosses back doesn’t guarantee unshielded hits. it is true, that an upper arrow hit/finisher hits no shields when standing in the back (like cyclone of steel, internal bleed, shrew blow, feint attack, bloodbath etc.) so it might be a good default position for DW barbs or Bear Shamans (that spam shrewd blow over and over again) but you have to stand at the enemy’s left shoulder to hit the unshielded back with Combos ending Right (Butcher, Conqs Whirlwind/Bloody hack; BS’s Crush Armor…) or at the Bosse’s right shoulder for Combos ending Left like Ranger’s Dot, Barb’s DoT, BS’s Blood Thirst etc.
Also for max value you might wanna place strong Combo starters in the back of the boss, like Shrewd Blow VI (left) or DWs Upheavel (also left).
So in Raids - where you wont have all the freedom due to blocking players, you can choose optimal default positions, in 6M-Content you could move around.
Default posis: DW conq → left shoulder
DW barb → back
Shrewd Blow BS → back
CA UB Bewilder Aether Theft BS → left shoulder
2H Barb → left Shoulder
Sin → all directions, but pure Combo Damage: back for Swift Strikes (since Poisons deal alot of their damage thru Dots and Miasmas)
Ranger → Right shoulder (Upper and Lower attack to the left then); or back for Pen shot (upper attack buff then via Upper arrow)