Better for what? Certain benefits (seating, boarding, baggage, etc.)? Earning ability? Award availability?

Without knowing what your particular priorities are, the thing the major difference that jumps out at me is that earning on AS is still done by BIS miles and fare class, whereas on AA it is based on $ spend. That might make one or the other program more 'profitable' for your international flights in particular, depending on where you normally fly and in what class. Also as noted above, AA has a greater number of non-flying ways to accumulate the points needed for ongoing elite status. That can be a good thing or a bad thing, again depending on your flying patterns. (In many instances on AA, it can seem like actual flying is the least profitable way to earn Loyalty Points, compared with other available options).