I'm using my buddies After Effects and I can't for the life of me get a clean subject to use. It's for a music video so I don't know if green screens can't handle a lot of movement, but here's what I have.
if you are using keylight (and it looks like you are), in the screen matte settings try setting the 'replace method' to hard light, that often helps.
another thing that are seeing is ae's quick and dirty pixel aspect ratio correction for previews. what you might try doing is setting the composition settings (composition>comp settings) and choose a square pixel setting for whatever format you are using.