A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 102,617
The OP's decision isn't just between *A versus oneworld but also which specify airline to use as the primary program.
Going with *A but not UA has some advantages, including getting access to UA lounges for all *A flights, including UA domestic, at the *Gold level. Obvious disadvantages are no free Y+ and no free elite upgrades on UA (and probably extremely low priority for OPUPs on UA), no UA upgrade instruments, etc. if high enough elite status is obtained.