The real time performance of the OS is going to make an impact on how well OpenCV will work.
From the tutorials I have seen online most people seem to be recommending the use of Raspbian. Raspbian is one of the more popular choices of operating system for the Pi. So one advantage to it is there are a huge number of tutorials for various things based around it. This means if you get stuck on something there is a much greater likelihood of finding an answer.
The downside to using Raspbian is for real time stuff is it simply isn't going to be as quick as a cut down OS like Minibian. However, if you look at the official Raspbian download page you will notice the most recent version of Raspbian is called Jessie. And that you have the choice between Jessie (With PIXEL) or Jessie Lite.
Jessie Lite is essentially a cut down version of Jessie. There is no Graphical User Interface (GUI), and comes pre-installed with less software. Setting it up to work with OpenCV might be a little more challenging than if you had a GUI. But, the benefit is OpenCV will probably run much better.
Having done a quick search for Minibian it doesn't look like there is many tutorials based around it. I'm sure you could still get everything to work, although I'm still inclined to recommend Raspbian Jessie Lite.