Differences between AForge and OpenCV
Solution 1:
Well, why not using both ;) ??
I am using (literally in C# ... lol) EMGUCV.NET (which is an OpenCV C# wrapper) and AFORGE.NET at the same time:
AFORGE.NET plus its "Image Processing Lab" makes much sense for filtering options (edge detection, thresholds, and so forth) and easing viewing functionalities.
OpenCV provides all the rest like SIFT/SURF and other more sophisticated image processing routines.
That's why you use .NET: simply bring all the components you need together in one application :)
Solution 2:
I am using OpenCV for a project in school right now, and I browsed the documentation for AForge and their feature seem to differ. AForge has lots of filters and is probably excellent for different transforms and image manipulation. But it seems to lack quite a bit in other areas. I could not find any matrix operations which was a disappointment as it is so useful in computer vision. Our current project (3D point cloud reconstruction from an image sequence) would, as far as I could see from the docs, be impossible to do with AForge alone.
Combine AForge with a good linear algebra library and you might have something really useful though.
As for OpenCV it has a rich feature set but is a bit tricky to program with.
Solution 3:
If you would like to improve your application with more and more advanced functions like you said, I'd go for OpenCV- however, a part of your success depends on the fact that the C# port is actively updated, which shouldn't be much of trouble considering the three ports. I think EmguCV seems to be one of the best right now in terms of updated, but when I looked at it, lacks documentation (but you could probably translate C++ code into C# with some C++ knowledge). AForge seems a lot easier for me and that's what I'm using right now. OpenCV also has support for haarcascade.xml files you can use that include face detection.
So for the final take: both will suit you well, OpenCV is more widely used/supported (though most user-base is C++), AForge is easier. It all comes down to what you want to do.