So I got lucky and traded a Venom,God Symbiotes for a Black Lantern Superman and traded a Joker/Thor Gwen/Darkseid Legacy rare for Hal Jordan BL, of course I then won a Hal.
So I played a BL/Porter team. If I played it correctly it seems very OP.
I played
Superman 120
Nekron 40
Hal 60
Porter 25
Porter 25
Indigo Ring on Porter Free
Sinestro Ring on Porter 10
I had points left over but it was a test run of what I had. Could played Black Hand or Lyssa instead on a Porter or changed values.
What is the optimal Black Lantern Build? This build got Nekron and Superman top dial on Turn 2! I chose indoor but coulda gone outdoor and still had protection thanx to Stealth but woulda been a risk if I rolled poorly.
Is Superman way to go over 2-3 BLs? Is twin Porters best option or another BL? I played these cause they are what I have. I ordered Batman,Wonder Woman, and J'onn J'honz already plus 3 cases.

Which Black Lantern team build is best?
So I think Nekron and Scott Porter are great starts. The question is who should fill out the team? I think Hal, Batman, and Super Man are the best options.
Build 1
Nekron 40
Scott Porter/Indigo Ring 35
Hal Jordan x3 180 Green Ring
Batman 40
This build relies on Batman to insure Hal Jordan can freely Pulse Wave without hitting the other Hals. Lotsa ways to control board and pace of game. Nekron becomes a Super Sniper by Turn 2.

Build 2
Nekron 40
Scott Porter indigo ring 35
Superman 120
Hal green ring 60
Batman 40

Concentrate on getting Supes and Nekron healed up first. Batman and Hal are support options. Superman is just a monster with Nekron finishing off any weakened opps.

Nekron 40
Scott Porter 25
Hal Jordan Green Ring 60
Batman x2 80
Green Arrow 50
Wonder Woman 45

Adding some diversity. Diana is good against Shape Change and has serious damage potential. Green Arrow helps Nekron with sniper duty.

Any other suggestions? Maybe a different theme like Monster mixed in with Black Lanterns? Hal is freaking crazy good. He brings so much.

Just to preface, I only collect DC nowadays - I may be a bit naive to other equipment or keyword shenanigans out in the marvel world that could change the math here.


The Core (corps?
I think that Nekron, Superman, Scott Porter (black shirt) with indigo ring is a guaranteed core. The fact that the difference between 120 point superman and 260 point superman is 3 clicks and Scott can heal him that turn 1... it's just mandatory.

That's 185 points, leaving you with 115 to work with. If you're playing this combo, it's likely that you're sticking with Black Lantern Corps to get Scott's Community tokens.

So from there, what do you build around? What do you need?


Secondary Attacker
Wonder Woman and Aquaman are a potent secondary attackers, but don't bring much else to the table.

Ollie brings prob, which is nice as Nekron will lose it with some healing, and is another great secondary attacker.


Hal and Manhunter stand out from the pack as potent secondary attackers that ALSO bring something else to the table - Hal gives Superman (conditional) willpower, has insane willpower himself (if equipped with a GL ring), and gives out tokens like candy. Manhunter brings his compel power to the table, as well as being extremely independent between his nasty shape-change, impervious, and stealth.

Utility
Scott Porter (white shirt) brings prob and another pulse wave, Lyssa Drak brings some interesting if not all too crazy debuffs - including a healing debuff, which makes sense if your opponent is playing black lanterns too. Black Hand brings perplex + tk to the table. Batman brings a powerful outwit and a way to hide from range. Plus he can start with the utility belt, granting all sorts of goodies.

Additionally, Batman and MM have the Detective keyword, giving them access to all of the wonderful mystery cards in the arsenal.

So given that, and given that Hal and MM are both 60 points and are probably a matter of preference, that gets us to 245, giving us the potent nekron/scott combo, a wild primary attacker in Superman, and a secondary attacker with lots of utility in Hal or MM. With our remaining 50 points, do you want:

To hide from range? Pick Batman.
To have more grave markers + TK? Black Hand.
An extra prob + potent ranged attacks? Green Arrow.
AoE poison for pesky bystanders? Aquaman.
Healing shutoff (because your opponent is playing BL too): Lyssa Drak.
Blades? Wonder Woman.

White Shirt scott is appealing at 25 points of the remaining 50, but without another 25 point option, there's nothing else to fill that slot.


Conclusion
So given all that, my team of choice would be:

Nekron (40)
Scott Porter (Black Shirt) + Indigo Ring (25)
Superman (120)
Hal Jordan + Green Lantern Ring (or MM) (60)
Batman + Utility Belt (50)
295 points, 5 more available

BTUMC006 Murder in the City Enduring (Hal Jordan, Batman, Martian Manhunter)
Give a BIG powerup to a single character. This is a fantastic addition if you have Hal and Batman, making use of that willpower and supes' leadership.

BTUMC007 Stakeout (Batman, MM): Grants regen to characters in hindering terrain. 'Nuff said.

So I like your thinking and came to a similar conclusion. Exact same conclusion except I didn't have Bat Belt. The Ring cost 10 on that Porter. I always healed Nekron first and hoped for a good roll. Then would base my next support roll and free heal on my opponents movements.
Then I tried the White Shirt out.
Superman 120
Nekron 40
Batman w/Indigo Ring 50
Hal w/Green Ring 60
White Shirt w/Utility Belt 25

So the whole team gets +1 Attack and +1 Damage. If I am able to heal Superman and Nekron up with 3 Support rolls in the first 2 turns or can see an easy KO it is golden. If Batman gets a willpower roll so I can have him assist on turn 3 his 12 for 4 flurry is epic. Superman is capable of 8 damage since the damage dealt bonus defies the rule of 3. The team requires good support rolls though and no +1 like H4H Scott. I like Batman and Hal cause they do not take support rolls. I use Steal Energy to heal them and keep them behind Superman til I can pull it off. They both make Graves relatively easy too. Not sure why Hal isn't getting more love. He does a lot. Nekron has Willpower on 2-6, Hal 3-6, Batman 4-6 as long as I have the graves. I might grab Stakeout and see what Martian Manhunter can do.
I do not have all the BTU Cards but may have to get them based on your suggestions.
I tried a Green Arrow with Skybreaker over Hal once but think Hal is better. Green Arrow needs to be healed and not healing Nekron is risky. The time I didn't and healed Ollie my opponent rushed Nekron for an easy kill.

You could always play TWO Nekron. I agree that Nekron should be the first character healed.

Is the Double Nekron a pair at 40 or a 75 and 40

Without considering any of the builds discussed so far, my order of preference would be:

1) One 75-point Nekron (I'm not that into dupes)
2) Two 40-point Nekrons (see below)
3) One 40-point Nekron (budget... but riskiest option)

I can easily see using only a single 40-point Nekron, but I would be worried about a bum's rush to KO it before it did anything... and then possibly being saddled with some relatively weak BLs. Note I don't have a BL Superman to draw attention/run interference.

My two-Nekron suggestion is half-motivated by insurance, and half-motivated by the giants' ability to generate GRAVE markers withing LoF.

Frankly, think this ability of Nekron that allows almost any friendly character to be "healed" past its starting line (even though it may take some team-building shenanigans) to be insanely powerful. I'm not sure it would be all that necessary to stick too closely to the "Black Lantern" keyword for theme teams.

I will have to try it. I started messing around with Monster and Hetald Keyword teams. Double Nekron might do good since I steer away from Supes on those builds.

I like the 2 Nekron if Superman isn't in.play as you said. I always heal Nekron first and choose an indoor map so I can Barrier him in at first. It has been a hurdle in some early games. I am waiting on Deceased WW and Supeeman.
I think White Shirt using 1 of them for leadership and a mix of Batman, Nekron, Green Arrow could be fun.