Brains vs Brawn (and numbers)

Batman and Iron man vs Justice League and Avengers

Batman and Iron man

• limitless wealth
• Genius level Intellect
• A year of prep
• The element of suprise

JLA/ Avengers

• Superman
• Hulk
• Wonder Woman
• Spiderman
• Aquaman
• Thor
• Vision
• Shazam
• Captain Marvel

Seems plausible

Jla and Avengers stomp. It is not like they are idiots.