Aquemini is one of the crispest sounding rap albums ever. Using it to prove how ATLiens' production sounds "dated" is fucking stupid. ATLiens is grimier because, like Domino mentioned, its budget was way fucking smaller. When the only artists you can afford to work on your album are a part of the Dungeon Family collective, it makes sense that the production will sound homogenous in retrospect -that's why it's a more cohesive product than Aquemini, imo. Aquemini is bubblegummy, incredibly polished, and much more indicative of the crossover-pop direction they were heading in. ATLiens was still firmly rooted in the gangster-gangster back and forth they'd established in Southernplayalistic but included an emotional depth that was possible because of the increased distinction between Big's and Andre's characters. With each successive tape they try to replicate that, and fall short because of the flanderization of both performers.
Broadly speaking, if you like the dirty south and/or identify as a stuck in the 90's ninja, you'll enjoy ATLiens; if you like the super glossy, super expensive aesthetic in the increasingly lucrative, but creatively flatlining landscape of turn of the millennium rap, you'll enjoy Aquemini. I, for one, enjoy both equally. Not out of a well-tempered decision I've reached, but purely out of spite for you guys who hold this debate every 5 months.