Matted or Unmatted??

Hi,

Here I just want to ask question about quicktime movie rendering. Maybe some of you can tell me which one you usually choose when you render quicktime movie in AE. Matted or Unmatted? I like to choose Unmatted especially my animation movie background is nothing (I mean, transparency...). However, have you guys meet the situation that unmatted movie looks weird in jitter playback? However, if I choose matted, sometimes my background color will looks different from jitter window background color.

What is the best way to use matted and unmatted render?

thanks