Read the rules
When submitting a video to a convention, one must be very careful to
read the entry rules so that you are submitting in a format that they
will accept. It is very important to follow these rules.
Follow these simple rules of thumb when deciding how to submit:
1) If they specify a preferred format make sure your video is in that
preferred format.
2) If they do not specify a preferred format and instead accept a wide
range of formats then submit using the highest quality format they
allow. If they allow a lossless format like HuffYUV then send them a
HuffYUV master on a DVD-R or, if they allow it, split across several
CD-Rs. This is especially important if they are going to be re-encoding
everything they receive anyway so that as little quality is lost as
possible.
Does the convention prefer MPEG2?
Most conventions do prefer this format. Scintilla has written a useful guide on encoding your video to mpeg for conventions, which you can read here.