Also build quality.. and as far as the s3 having a big battery... 3000mah and a much bigger screen...
Yeah we don't know how efficient the processor will be, but with as many tweaks as they've added to touchwiz, its gotta be heavy and very taxing on the cycles of the processor.
Perhaps I'll be wrong... but i'd bet the maxx should have a lot better battery life.. we'll see though... I don't know a lot about Samsung devices.
3800mah battery with a 4.7 inch screen, lighter (near stock) ui, stronger radios vs 3000 mah 5.5 inch screen, heavy touchwiz, quad core, 2 gigs of ram.