I'm no expert on AsiaMiles but the first level is I believe 30K, so did the 25K come from current flying? If so, I'd certainly consider that fact in my decision.
If your flying pattern normally includes SEAsia and/or Australia, the call between the two is more difficult as posting on Flyertalk indicates that CX does take incredible care of its own FF members. And upgrades with miles are relatively easy. And allows the use of premium cabins and status earning simultaneously. Remember you have to register for MPC separately.
OTOH my experience with AA has been quite good. And if you fly long haul economy, gaining and keeping status is quite "possible". And currently the award flights with AA are "economical". Lifetime status though is now going to require a LOT of BIS flying.
Happy wandering
Fred
95% LTG (AA)