Filter Help

I have the Corkin A series filters which I used with my old 35mm and my Sony cameras.
These will not work with the 20d.

So my question is should I just go to the Corkin P series filter system
or should I look into other systems like Hitech,Singh-Ray or what about the Lindahi system there are others.

Now seems like a good time to pick the right system since I have so much invested in Canon glass.

Any thoughts on this ?

Thanks for the help
Fred