It all depends on where you want to go with your miles. AA allows two stopovers (one at the domestic gateway and one at the foreign gateway) and an open jaw. Want to go to CDG, then to PRG, and stop in YUL on the way back? AA miles let you do that.
I do like the Star Alliance hubs in Europe more than Oneworld's. VIE, WAW, FRA, MUC, OSL, and LIS make it relatively easy to always find some availability. I use my miles for business or first class tickets that I couldn't afford to buy with cash. I would rather fly many foreign carriers in J or F before either AA or UA in J or F, and I usually have good luck finding space on LH.
However, I value US miles a little more than UA miles. If I go to Australia, I'll try to fly either NZ or QF, both of which I can get using US miles. Also, if you want to go to Asia but can't find *A availability over the Pacific, US will let you fly via Europe for a small premium (15K for business class). That gives one a lot more options.
All in all, I like having a bunch of miles in a bunch of programs. I just booked IAD-FRA-VIE,VIE-FRA-MLA,MLA-FRA-MUC(stop for 21 hours),MUC-IAD for New Year's using US miles. That worked out great because my GF needs to start in DFW and end in IAD, so she was able to get DFW-FRA-VIE,VIE-FRA-MLA,MLA-FRA-MUC,MUC-IAD,IAD-DFW and she'll just skip the IAD-DFW segment. Oneworld does not have any flights from Europe to WAS that can be had using AA miles, so the GF would not have been able to leave from DFW and return to IAD using AA miles.