I prefer the Huffyuv codec in Poser. Lossless compression, so I can postwork and edit the video, and have a smaller file at the same time. It even supports the alpha channel. You have to enable the "Always suggest RGB format for output" option, however, since Poser doesn't natively use a YUV colourspace.

When done, I convert to DivX or MPEG with third-party utilities, also.