The access to F lounges as a OW Emerald is great. Also, for the business class travel options, BA and CX (in OW) are great, together outweighing SQ (in *A). As has been noted, though, the BA option doesn't exist if you're an AA member wanting to redeem or accrue TATL.

OTOH, *A has many more partner options in most of the world, with the notable exceptions of South America and Australia.