I personally use 4 or 5 different Raw converters depending on the requirements of specific images and of my vision for each image. I don't need more than that!
Interesting point, Alain. It's highly unlikely that any single RAW converter will be better than all the otheres at everything.
Whist I currently tend to favour RSP over ACR, there are certain images with deep shadow noise, for example, that seem to be better handled by ACR. The 5D in particular can produce significant banding or streaking in deep shadows, whatever the ISO, but clearly more of a problem at high ISOs. ACR 3.3 seems to do a better job than RSP at removing such banding.
A plug-in for RAW converters is a great idea.