which does not apply here
Taking Soldier as your second class when you already are a Nightblade has a very high opportunity cost. The classes are too similar in the wrong way (the way they play) and too dissimilar mechanically (say in terms of damage types).
nonsense. They are similar in how they play and compatible in damage types. That there is some skill overlap is true, but since you are always strapped for skill points anyway, that is actually a good thing, so opportunity cost is just fine
Conjurer isn’t limited to just that.
You can make a lightning conjurer as well besides the vitality and bleed builds.
Not going to argue here, sorcerer is capable of melee, ranged and caster
Not at all tricky to build around.
Ulzuin’s Wrath is not worth more than a point.
Move speed is pointless for any build, attack speed is the thing you need to work upon here.
Vindicative Flame, Blast Shield and Flashbang are a must.
Night’s Chill is not necessary on all Sabos.
Poison Sabs can be easily built. I know i have one. And there exists an Acid Sabo on this forums posted by edinosian.
Life drain is irrelevant, can be achieved through any build that has high %weapon damage.
Physical Elementalist is a waste of time.
Lightning Elementalist is powerful.
Pet support is limited in an elementalist
You have no idea what you’re talking about. Blademaster is the single most powerful combination in the entire game. Stronger than a Witchblade.
Trickster, is tricky to build around.
One can make a good trickster. It’s tricky but still doable. Bleeding trickster is pretty straightforward, Lightning Trickster is a little hard but a nice challenge.
Squishy till the end actually, hard to build w/o good gear. Poison Warlock, Aether Warlock, Chaos Warlock are some things that come to mind.
Now the things you missed.
Witchblade-
Great class combination. Physical WB is really strong. Chaos WB is even better (well i mean it’s much more cooler)
Warder-
Supports Lightning, Physical and Bleed. Insane HP and tankiness
Commando-
I keep getting the feeling this forum hates Commandos. Fire Commando is pretty strong, and recently Supefluff’s Temper Commando shows us how strong physical commando is.
Pyromancer-
Chaos/Fire synergies. Really unique playstyle. Can go dual-wield ranged or dual-wield melee through items found at Devil’s Crossing vendor. Powerful class combo
Witch Hunter-
A lot of builds are possible, but the best one (actually my favorite one) is a poison witch hunter. Can go DW-melee, DW-caster and Focus-caster. You can also go ranged with it.
Spellbreaker-
Caster and DW builds possible here. Cold/Pierce or pure cold builds. Powerful in its own right.
Druid-
I haven’t made one yet mainly cause i don’t like TSS. But that doesn’t mean Druids are bad. TSS Lightning/Cold Druid is a pretty strong class combo
Battlemage-
Shit, Shit, Shit. Nothing unique about this class combo. Anything Battlemage can do another class combo can do it better.
It is as JoV said, you have no idea what you’re talking about. I am guessing you’re judging synergies based on the skills you saw. And never played with them to see how the synergies work in practice. And i am guessing you have no idea about the various item sets that support these class combinations nor the conversions that improve synergies
I was referring to a specific type of Cadence + on proc dual wielding build. Nightblade has absolutely zero skills that deal Physical damage aside from weapon skills which every other class also has in some shape or form (Shaman or Demolitionist are infinitely better). So the opportunity cost applies.
The only damage type Nightblade and Soldier have in common is Bleeding and not only Shaman + Nightblade allows a much better Bleeding build but also many monsters are immune to Bleeding.
You appear to forget that a Blademaster can convert Phys->Pierce to greater effect than any other mastery pair.
Convert, how so? You mean Fighting Form or Deadly Momentum?
I mean the % Armor Piercing stat found on weapons and increased via Devotion/certain gear/set bonii.
But these are not specific to a Blademaster, are they? A Saboteur or a Commando can still do the same thing.
Is Battlemage really the worst? I came up with a Tremor Battlemage the other day: http://grimcalc.com/build/1006-QzDu9b + Arbiter using Obsidian War Cleavers. Now I am again exited to try it out. 
But neither a Saboteur nor a Commando would make as good use of it as a Blademaster. I’ve a Pierce build of those three combos (and a Trickster and Spellbreaker)
Omg…
Now really browse trough this:
http://www.grimdawn.com/forums/showthread.php?t=47967
http://www.grimdawn.com/forums/showthread.php?t=48091
http://www.grimdawn.com/forums/showthread.php?t=48783
In those builds Im using phys to pierce conversion. Im converting flat phys dmg from cadence, deadly momentum, devotions and equipment to pierce.
Just for record and for you to know phys dmg, due to items available in game, is easiest to convert in any other type of dmg.
Also I understand people enjoy playing a certain concept.
Amarasta’s Blade Burst Crossbow Trickster who happens to spawn Wind Devils and create ligtning torrents was really fun to play as. Certainly was not the strongest combination in the game.
I am trying to argue strictly in terms of ease of numbers and all-around usefullness. A specific build of Blademaster can be the best Nemesis cutter in the game. That does not necessarily mean it is the best build against crowds.
Yes they can but its not that efficient. Only dmg that you can convert from demo is flat phys dmg from temper. Yo cant convert fire to pierce.
The gear you are using is not specific to a Blademaster. Demolitionist has a Piercing damage amplifying skill, so a Saboteur would have better piercing damage.
Also I looked at your build and I did not like it. You and I certainly like different things and that is ok. I like maximizing things and keeping the builds concise. Yours is way too spread for my taste. But if we are going to argue purely in terms of numbers, that is survivalibility and damage per second, I would argue any build you can come up with can be better done with a Commando or a Saboteur.
The trouble is that you’re asking for the best and worst classes, of which there are builds that perform very strongly and others that…well…don’t. Speaking on average of those, the “correct” answer for best has already been given: Witchblade. Battlemage is largely considered the worst because it possesses and unfathomable amount of antisynergy between its skills and itemization. Between these two classes are hundreds of builds that excel in various areas to varying degrees.
You dont have trouble with crowd as a blademaster, you have lot of procs that deal with them really fast and efficient. Ie blades of wrath/blade spirit combo, blind fury, ring of steel, some wps procs like BS and WD (if you need them i personally dont),…
Its not about liking something or disliking, you lack the knowledge, period.
In terms of numbers when you make some sabo or commando that can put down dummy in less than 25 sec we can talk, till than try to learn something about game mechanics.
I have a pierce sab and i can say it’s inferior to BM in terms of single target damage
Since when does hitting dummies mean a build is super strong? Dummies don’t hit back. That’s such a terrible measure of a build
I maybe misunderstanding what you are saying, but you seem to be ranking the classes by themselves with no item and devotion support. That’s not how it works, item and devotion support play a role on how much effective a class combo will be.
Blademaster gets a lot of item and devotion support and that combined with its skills, makes it a very effective class.