If i edit something shot on green screen and edit the mxf files, and then want to export it to do the keying what is the best setting to use for the same quality?

should i use avi uncompressed? or mpeg2? or 4?

i use premiere pro

What software are you using for Keying?

If in Premiere then you can open native EX files without having to convert to MXF.

Are you wanting to export at Full HD or as a SD avi?