Star Alliance and oneworld seem to keep one-upping each other, but I think over all, they're both similar. You'll probably find more diffences between two carriers in the same alliance than you would between the two alliances.

As far as upgrades go, I think the only airlines where there is consistent reciprocity is between Canadian Airlines (CP) and American Airlines (AA). CP and AA members can upgrade on either airline, using upgrades from either airline. Has worked very well for me, so far.

My experience with oneworld, in terms of hassel free travel, has been very good. Once in awhile, I won't get all the perks that I think I should get, but usually it seems to be related to the newness of the alliance. Others have also reported similar problems (i.e. CX giving preference to a CX 2nd tier member over a CP top tier member, contrary to the stated oneworld policies.)

Having said that, I think right now that oneworld is winning the ease of travel battle. But it's always subject to change.

Regards,

Ken Hamer