...the movie was a soap opera. I'd even say she's the hottest superheroine since 1992. The bar wasn't high since then, though; Malin Ackerman's Slik Spectre II was probably the closest second.
Since I stopped around the 20 minute mark, now the important question: did Elektra sleep with Abby's dad? Or with Abby?
Mmmm...disagree on your evaluation of Elektra/Garner's level of hotness.
One of the top contenders might depend on what you consider to be a "super hero", though. Catwoman has always ridden the line between (anti)hero and villain, but if you're counting her, then I'd say Michelle Pfieffer has got to be at least in the running.
Margot Robbie as Harley Quinn was pretty hot, too. Scarlett Johansson as Black Widow and Famke Janssen as Jean Grey would be in the running, too, no?
If we're counting Michelle Pfieffer's Catwoman, then that is probably our winner. She was super hot and memorable in that film. More so than anyone else you named.
As for Garner, she was definitely in great shape for this film, but I've never found her face to be A-level. She's attractive, yes, but not top tier.