My advice is always use the progressive format for gaming. As you are seeing the whole image per frame. But, go with what looks best to you.
Also, if it were an LCD, DLP, or Plasma screen (IE, Fixed display) there would be no such thing as a 1080i set. 1080i monitors are generally only 720p, they just "downscale" 1080i to fit the 720p display. Remember that an interlaced resolution is actually only displaying "half" the horizontal image per frame (Frame 1, odd lines, Frame 2, even lines and so on).
But, I have a feeling that your TV is actually a 720p set. It's not very common for there to be a rear projection set (I doubt it's a 60" tube) that is running 1080i natively. Generally you only see that in "higher end" (of their time of release) front projectors. But I could be wrong.