Hmm... This is almost a loaded question in some ways.
For myself, in terms of overall execution of the character both for the show itself and as an adaptation I will have to give the edge to Frank/Punisher. We got into his inner life which added meat onto the bones of my own personal conception of the character. They fleshed him out well and he seemed both like a real person and a larger than life comic book character. I totally agree that Berthal's Frank deserves a show of his own.
Elektra, for myself, well... I have never really been a fan of the comic book character. She always seemed very much a cipher to me, even in the original Miller stuff, and then post her resurrection perhaps even more so. So I had no high hopes for the character on the show really. I hoped she would be a good femme fatale, ruthless and with some charm. And... She was. Now I agree, as a person if she were real, a little of her as presented on the show would go a long way. I too can often chafe at certain characters that simply... Aren't nice. I get wanting to "like" a character that you as a viewer will be spending hours watching. But the vibe of DD as a show, well... I think it fits. Stick is not nice or really likable either. Hell, sweet Foggy got on my nerves sometimes, but in trying to make a show that feels "real" that all works for me. Elektra for sure is pill, and she has probably been off her rocker for a LONG time as intimated by the show. But, again, that all worked for me and didn't grate.
In the end though, yeah, I came away with really looking forward to more Frank and could wait a whole other season without her until they decide to bring back Elektra.