I agree with Mak, gridiron is much easier from a tactical perspecitve because so much more is pre-determined - the blocks, the receiver routes, defensive zones. But gridiron is probably more difficult from a animation perspective because of collisions, shedding blocks, gang tackles, etc.
I sometimes feel Madden has not changed by much other than animations and graphics. Some better defensive decisions have evolved but the offense is still the same. And a damn linebacker 8yards from the QB can still intercept a ball meant to be thrown 25yds downfield. But they have done good at removing defensive backs having eyes in the back of their head that enables them to turn and intercept a ball just because the are there.
I think the items that make football a more difficult game to program/code are the same items we complain about on daily basis. Players not taking passes, not making runs to get open when we expect them to, keeper decisions, overalap, etc.
I need to check me out some basketball. I would be interested on how the game deals with pick and rolls and all that fun stuff.