I get that question a lot. They are both very different rings.
The "Q"-Rings have a much less 'aggressive' ovalization than the O-Symetric rings do. Accordingly, they are much easier for any rider to get adjusted to. In the basic 'road' orientation, you may not even notice the difference when you switch from round rings. In addition, it is quite easy to switch back and forth between the "Q"-Rings and the round rings. For several years, I was on the "Q"-Rings on all of my bikes. I believe that there may be an advantage for certain types of efforts. Based upon my review of several season's woth of SRM data over the same Interval courses, as compared to round rings, there might be around 1% difference for 2-minute efforts, but not the reported 4% (for me). Fron the pespective of shifting, the "Q"-Rings are fine on either mechanical or electric. I would be suprised if you would notice a difference. They perform equally well on Shimano and Campagnolo.
O-Symetric rings, on the other hand, take some getting used to. I would recommend starting with them on the off-season. Once on them, you will find switching back and forth more difficult. Unfortunately, I do not have a lot of data on them yet, but from an anecdotal standpoint, a number of pro riders swear by them. Having said that, my rings come to me second-hand (like everything I have) from a pro rider who switched back to round rings after several seasons on O-Symetric. He felt that the O-Symetric rings were affecting his 'snap'. With respect to shifting quality, the O-Symetric rings definitely take more adjusting to get right. Di2 seems to make really short work of any difficulties, though. I have not tried them on a manual bike yet, nor on any Campagnolo bike.