I really don't like this poll's options. They are very very limited.
I wouldn't do a series that has storylines that can/should be covered on Arrow. Birds of Prey, Suicide Squad, Catwoman and Nightwing would make great Arrow storylines and the kinds of storylines that show would cover would be better on Arrow with more established characters, and thus you wouldn't have two shows going through different vigilante/espionage storylines so that there'd be nothing to do by Arrow season 4 that hadn't already been done on Birds of Prey or Suicide Squad.
I wouldn't do anything that fits on Flash for the same reason. Firestorm is a Flash supporting character, as are anything metahuman really, as that is the CW-verse source for superpowers, the Particle Accelerator explosion. Flash is the king of that world, and that's really cool. Let him be that. Again, same thing with taking metahuman storylines and splitting them between two okay shows instead of making one incredible show that allows the Fastest Man Alive to literally run the gamut.
For a similar reason, I wouldn't do anything Batman or DC Magic related, because Gotham and Constantine will be using a lot of that stuff, and you don't want to be redundant, y'know.
I also think the 'trinity' of the CW-verse shouldn't be three white guys. A female or POC or both would be preferred.
A team show has potential, but that just seems like a roundabout way to focus on a white male character again, just with the supporting cast now having powers and the show being called a team name.
I wouldn't do Martian Manhunter as a CW twenty something angst fest. That doesn't feel like it has any chance of capturing the heart of the character.
I would enjoy a Green Lantern show, and I think that might be possible. The catches are, if it is possible, it's *Barely* possible, with little room for error and that it may not be allowed by WB based on their plans for Green Lantern going forward. As such, GL might not be the very best call.
My suggestion:
Kendra Munoz (female POC), dealing with reincarnation (supernatural shenangians, but not magic) and Thanagarian heritage (aliens and sci fi), taking inspirations from the Thor films (electrified mace! warrior ragefighting!), while having a very different powerset from Arrow or Flash and making a clear Trinity analogue.
Batman -> Arrow
Superman -> Flash
Wonder Woman -> Hawkgirl
Also a very affordable powerset, freeing up money for crazy villains and such. Interesting family relations: Grandfather 'Speed' Saunders, daughter Mia for momma bear power, throw in some DC standbys like Tawny Young, Snapper Carr and Susan Dearborn (dating pre-elongated Ralph Dibny?), put her in a love triangle between Carter Hall and Dr. Anton Hastor, DC aliens as the big bads per season, Kanjar Ro, Despero, Starro, with her and Hawkman's villains and those from the All Star Squadron as your baddies of the week.