But if you want the highest of the high level of graphics, super AAA quality rendering, then OpenGl is inferior. Maybe the latest version is great, but the ones I tried were a lot behind. For starters, a big chunk of OpenGL is implemented in the GPU driver. There is a huge quality gap between supper cheap GPUs never meant to do real rendering work and high quality stuff.
I can't offer you a citation, only anecdotal evidence.
In historic order:
1. Linux. This is probably the problem of early Linux drivers and not a real problem with OpenGL, but OpenGL reliability on Linux was very bad. Sure, if you ran glgears there were no problems. But if you tried to do more complicated stuff, some things would not render exactly as expected with no way to fix it except to either try to change X setting and mess around with the driver or move to another PC. There were small bugs that effected only parts of it, allowing you to render the scene but some effects would not show up.
2. Windows Vista + some ATI cards. When Vista came out, some ATI cards had broken OpenGL drivers and it took so many months for them to fix it that I gave up on Vista. The performance was very bad.
3. Even today, there can be subtle differences. Things like Toksvig specular AA are highly dependent on the exact behavior of the GPU filtering system. Even right now if I tried, I can get at least 3 different results on 3 different PCs. Same code, same resolution, different GPUs. The probability of getting it pixel perfect is less than in DirectX and OpenGL has no mechanic to report to you that it is doing stuff differently than you would expect. It says: OK, rendered corectly! And indeed there is output on the screen. And if you examine it superficially it looks OK. Maybe just by a little and I had bad luck. But I'm pretty sure it is not higher.
What I got out of all these experiences is a common theme of slightly less reliability. This is of course an issue only on the PC. If you target some hardware that only has OpenGL and historically has only had OpenGL and everybody is using OpenGL do do 100% of the graphics stuff, there will be probably no such issues.