I'd be open to buying both as well so long as they look good. The only one on the list that would be a firm no for my JL line up is Cyborg. He'll always be a Titan in my book.
I actually do like the character but he will ALWAYS be a core member of the Titans to me. I have the entire Wolfman and Perez runs on the book and just can't imagine the Titans without him. Out of all the new 52 changes, making Cyborg a core member of the JL really upset me. Oh well, I just read the Bat books now anyway as far as DC is concerned. The reboots over at Marvel & DC have got me reading a lot less comics.
The Flash is my favorite DC hero, so I will cast my vote for him.
I also definitely want to see Aquaman, Hawkman, and Martian Manhunter. Another hero that's not on the list...Firestorm. I'd love to see a Firestorm PF.
I am thinking Aquaman or Flash. After they do those two and get the main JL out of the way, I am hoping for a Nightwing and some more supporting characters.
They need another woman already. But first, I would just like them to concentrate on getting Superman out on time so will be hoping for that first. My vote is Wonder Woman or Catwoman but I don't want any thick cluncker men's boots on Catwoman this time They better be hot!
Based on popularity it should be Flash. However, while not my favorite character Aquaman would make a great PF. I would definitely like a Martian Manhunter. He is the most constant member across all iterations of the Justice League. Also hoping for a Doctor Fate someday. Great PF potential.
Aquaman wielding his trident would look cool. I'd get that of done well. Flash is a given, not if but when. Hawkman might make an interesting looking PF as well.