Superman
Batman
Wonder Woman
Martian Manhunter
Flash
Aquaman
Green Lantern
vs.
Flash (original)
Alan Scott Green Lantern
Stargirl
Hourman
Hawkgirl
Dr. Midnight
Mr. Terrific
Wildcat
Power Girl
Dr. Fate
I'm not sure who would win, the JLA have the telepathic advantage with Manhunter and have more all around uber characters, while the JSA have a couple big heavy hitters and more people. If Captain Marvel and Black Adam were still on the team, it would be a sure win for JSA, but they recently left, but I think with Fate, Power Girl and Scott they have a good shot to take the JLA out. I'm going with JSA as I do lean towards the Golden Age characters a bit.
The JSA is rather large. In most cases they have had black adam, captain marvel and atom smasher and power girl on the team. They are heavy with power. Not to mention J. J. and his geni or alan the green lantern or dr. fate. I know that atom smasher and black adam may not be on the team. But even without them they are top heavy with power and have quite a few thinkers, midnite, terrific, and hourman. And of course sand is an x-factor. The JLA is a great well trained team. But the JSA outnumber them.
The perfect post. I'm saying everything this guy said. Adding, without Captain Marvel, they don't have a superman on their team that could handle the original, but that's ok, because the good Doctor can hold him down with magic.
Oi, and Alan Scott is the greatest GL ever. Bitches.