The deculture edition was released in late 2007. I think it was a "teaser" of sorts to get people pumped up for the series. The broadcast episode 1 is very similar except for a few different scenes. For example, in DE the VF-171 launch is choreographed with Sheryl's concert song while in the BE it's separate. The concert is also longer in the BE with new scenes. The DE also lacks any opening or ending songs, which the BE has.
Some criticize the BE as being a bit inconsistent in its scene editing, but it's not that bad. IMO, watch both to get a full picture of episode one, since you have scenes in one that aren't in the other.