And I personally rate Zoltan A higher. Although I'm not as confident about this, than about Crystal B > Lanius B.
Well the weapons are impressive and you can make your shields pulsar-proof right off the bat, I'll give it that but it's the Zoltan A. I don't like the Zoltan ships very much. Especially Noether. (How dare you make the high-scores on Normal! How dare you have a decent run!)
Lanius B has two primary weaknesses, that I see. Early game, not being able to suicide your boarders with asphyxiation can lead to a failed initial assault due to low health, and slower victories. And slower victories lead to more hull damage, and a higher chance of a meltdown with unlucky system hits. And while the Shrike flak cannon is incredible, it has the drawback of being somewhat less able at targeting specific enemy systems, like weapons.
Open all doors except for the Pilot and perhaps Oxygen. In a pinch, open up Pilot. If they board, they go for oxygen. Close the doors at the Clone Bay or something. Then open doors at oxygen. Crew sees oxygen running out before they get there and walk the length of the ship to the Clone Bay. Seal Oxygen, open Clone Bay. Repeat until boarders dead or your Engi pilot suffocates.
As for Weapons, you Mind Control guy on shields, send boarders into shield room. Then move Lanius to Weapons while the enemy focuses on the shield room. Or don't, let the Flak take care of it.
Or Mind Control pilot, then teleport pilot back to your ship to be suffocated.
And on the other end of the spectrum, having only a 2 man room for boarding makes your later assaults weaker/slower, while reducing your ship to ship combat (as hacking + cloaking is ideal).
2 Lanius is all you need

And Cloaking. Only because of the Phase 3 Death Blossom.
I might be wrong, and maybe someone can prove it by having an incredible record with Lanius B :p. Then we can ban it and go for 3rd(?) best, below Crystal and Lanius B, whatever order those two are.
I'd say Red-Tail but... I never won a game on Hard with it. I mean how could I possibly mess up 4 laser barrages?
Let's go with the Slug C. Only because hardly anyone unlocks it because they got to play with the Slug B(ad).
But I never got a high score with it, compared to my Hard and Normal Crystal B runs (seriously, my list is this: 2 Lanius B, 2 Crystal B and the Zoltan B at second-last place)