Flash - Hes just cool. And keeps some humor in the group. Plus with his speed, he can get anywhere faster than any other member besides GL.
Guy Gardner - The rebel of the group. Almost as powerful as Hal.(more powerful in some ways). He takes all the attention away from Flash.
Captain Marvel - To take the place of "Big Blue", you got "Big Cheese". This gives Billy the chance to show hes mature enough to lead a team or at least be the head guy in charge.
Zatanna - As one of the top magicians in the DCU, it doesnt hurt to have her as a full-time member od the JLA. Plus I love her. Hope she gets her powers back in SS.
Martian Manhunter - This guy has many powers at his disposal, but he doesnt get enought recognition in the League with all the "Big Guns" Plus hes a powerful telepath. A team couls always use one of those.
Batman - Every team needs the "Sour puss". With Flash and Guy on the team, someone has to keep order. Plus Bats always has a plan. Hes also the groups preparation specialist.
Nightwing - Batmans figuring hes getting to old for the JLA gig, and decides to get someone to take in place with time. Dick is still the future of the "Batman Legacy". He sees this as the perfect time to get into the big time group. Nightwing and Wally are best friends as well, so he welcomes the invite.
Power Girl - With being in the JSA, she wants be be around a younger group of heroes. With he abilities and strength, he'll be one of the JLA's biggest asset. And her boobs too.
Starfire - She provides the love intrest of the group along with great power. I also see her causing alot of problems within the League. Mainly with the guys. Woof woof!