As I continuously tweak my army, I tend to try out different ideas that don't end up on your standard internet lists. Today I take a look how the standard power sword stacks up against a single lightning claw. The results are unexpected, but not for the reasons that are obvious.
**Update: The original math had some significant errors that have now been corrected**
There are many arguments that power swords are not a good option, but in a meta that is marine heavy they remain a popular and viable option. Since this is the exact price of a single lightning claw, these two can be directly compared.
A power sword can be combined with a bolt pistol to gain an extra attack, but the single lightning claw will let you re-roll your failed wounds. The power sword can potentially kill more models, but the claw is going to be more reliable at wounding.
I started by looking at the average number of wounds (what most people consider MathHammer), and in most cases the lightning claw caused more wounds. The only times that it didn't were against toughness two and toughness three opponents.
However, average number of wounds isn't a reliable way of looking at this situation, so I ran things again but this time I looked at the chances of causing each distinctive number of wounds (i.e. 0 wounds, 1 wound, etc.)
A big thanks to Jeremiah Morgan for finding such a massive mistake in my numbers. I had a significant copy/paste error in my original spreadsheet, and I did not catch it myself.
I also wanted to bump what Jeremiah posted in the comment section, because his analysis is spot on and I couldn't have said things better myself.
The general rule is that swords are better against T3 opponents or when you only have 1 base attack. Otherwise, the claw wins out in nearly every other scenario.
The gap is going to widen in favor of the claw with every additional base attack that you have. So your chaos lords and various equipment or buffs that increase your attacks will ensure the claw outpaces the sword. While the inverse is true as your strength goes up, but less pronounced. I didn't run any simulations with hatred thrown in the mix.