Disclaimer: I am not here to pick on anyone's favorites here. What follows is just basic observations based on a good bit if trial and error. I am by no means an expert so if I get anything wrong then please by all means feel free to correct me. With that out of the way here's the companions listed from worst to best based on how useful they are in combat.
Note: I will not be taking into account specific unique or rare items that tweak certain characters into borked proportions of silliness such as the warped headband of intellect and such.
Shadowheart : I did say worst to best and well somebodies gotta be here so my apologies to anybody that really likes her...Maybe i'm just not seeing it, maybe with some uber speccific build she's really really great at something but with all that being said....
Using shadowheart on my squad just feels like deliberately adding an unnecessary liability to a team of assets. Everything She does well, other people can do a better and everything she does poorly just makes me feel like an idiot for bringing her along when I could have brought somebody better....
Pros:
-Healing and support spells.
-Decent durability.
-Has mirror image which can make her really hard to hit sometimes.
-Can facilitate ambushes (sometimes)
-Is pretty which in combat helps with... Uhm... Okay look I'm running out of pros here and the cons list triples the pros here.
Cons:
-Generally poor damage.
-Limited weapon options.
-Usually misses with damaging spells and cantrips unless somebody else sets up the target for her.
-Support spells call for concentration...
-Heals are completely negligible and replaceable with food, potions and just not taking damage in the first place through proper tactics and clever positioning.
-will usually miss most melee attacks and if she doesn't then the dmg will be negligible at best
-Burns a LOT of spell slots and needs to rest pretty often just to keep the things up...
-Most ambushes can be setup without here by using good ol'fashioned stealth so her stealth spell is of very niche value.
-Not particularly mobile
-Not particularly great stats.
-unreliable in close quarters combat
-Pretty sure the goblin clerics are better...
Gale : I used the word "liability" before and I'm probably going to use it again here. Gale Is a liability and even a potential threat to your own squad.
That said he rates out higher than shadowheart for his usefulness in combat and the environmental utility that he brings to the table.
Pros:
-He has decent ranged damage (when the spells hit)
-He has a pretty solid array of environment altering spells and abilities.
-Has plenty of spell slots and can restore the things without resting.
-Has access to a wide array of damage types.
-Nifty utility spells like feather fall and such for interesting maneuverability
-Is a legitimately nice guy who does not spend all of his time winging and disapproving when I help people instead of being a self serving opportunistic jerk (Glares at Shadowheart...)
Cons:
-Misses, a lot.
-most spells don't deal that much damage.
-He's really squishy unless you waste a turn with a defensive spell or cantrip followed by the next turn that you will likely waste on not hitting your intended target.
-He will literally damage and potentially murder anybody nearby over time if he dies which happens a fair bit as most enemies seem to really hate poor gale here.
-poor melee damage, I mean yeah that's not what he's here for but it ought to be mentioned all the same.
-really bad weapon selection, hope you like staves...
-He eats your uncommon magical items! Seriously I like gale but he really does not pull the sort of weight that justifies the sacrifice of powerful weapons and artifacts which in turn damages the parties overall effectiveness.
Wyll: The legendary blade of frontiers Wyll brings Eldritch blast spam to the table and that pretty much covers it.
Alright fine there's a little more to it than that. Bringing Wyll along always feels like a reasonable option, what he lacks in utility and variety he makes up for with reliable damage and stellar positioning.
Pros:
-Eldritch blast deals a lot of reliable damage.
-Has nifty warlock spells.
-fantastic battlefield maneuverability.
-Can use Rapiers.
-Surprisingly durable for a caster.
-rolled high in charisma because this guy is charming as hell.
-He does not consume magic items
Cons:
-Eldritch blast, you end up using A LOT of it, kinda dull...
-He's a caster and therefore squishy.
-Doesn't have a lot of spell slots.
Lae'zel: Okay here's the part where I'm gonna look mighty biased. But Lae'zel is an absolute beast and a very easy choice for frontline murder. No matter what squad comp I went with or what class I played Lae'zel was never anything but a solid choice. Yes she's a ruthless monster but oh my gods, if she doesn't reflect that to such an exceptional degree in combat. Having used her as a battle master more than an eldritch knight the following will focus more on battle master.
Pros:
-Excellent armor and weapon selection.
-Fantastic close quarters damage.
-Reasonable ranged damage.
-will generally hit what she's attacking.
-Is bloody difficult to bring down with second wind.
-Is strong as an ox, capable of lugging several barrels of explosive/flamable stuff as well as being able to frigging donkey kong those suckers to the nearest torch/candle/campfire source of -------ignition which covers a wide area with freaking FIRE! even more so than gale...
-Gets some nifty support and control options as a battle master.
-Has superb mobility and can jump like a frigging flea.
-Is literally the character in front of all others on all of the promotional stuff as well as the first companion you actually see.
Cons:
-Is exceptional at all things and willing to constantly remind you of that "fact"
-Is completely without any cons.
-Okay fine, her ranged capabilities are not stellar compared with rangers or other dedicated raged types.
-Not particularly stealthy.
Astarion: Okay since Lae'zel rates so absurdly well, I'm guessing you probably want to know what makes this guy better right? Is he some sort of god? Well, no...
He is however and indispensable problem solver. Need something dead? Send the vampire, need a few less things to murder in a big fight? have Astarion quietly remove a few things. Beforehand or just shove somebody off a cliff, they both work really.
Pros:
-This guy has the skills to pay the bills, seriously pickpocketing gold off those vendors really helps with buying weapons and supplies off of said vendors. Which translates to better equipped squads that are overall more effective
-Damage, he has it. near, far wherever you are he has the damage.
-Utility, yep especially as a thief, just start throwing things and poisoning stuff, it's great.
-Oh, did I also mention he's a vampire so he's eve got a free heal/buff from draining enemies which leaves them debuffed.
-Stealth, this guy has it in spades which makes for fantastic positioning and setups.
Cons:
-Support skills? Nope.
-Has vampire problems, don't fight in running water.
Overall the more magic oriented companions just feel weaker and ultimately more inefficient than the physical oriented companions.
I can handle a bit of inefficiency if the returns on it are worth it but, presently they just dont seem to be.. The real shame here is that because the gap is seemingly so wide, that as things are, I just have no good justifications for going out of my way to use Gale or Shadowheart let alone using them both for that matter.
Naturally I could be completely wrong but if that is the case by all means let me know.
