theres nothing wrong with either proggy but winrar is smart.
Pictures don't compress like you think. theres nothing to compress.
that would be the normal except to convert. that make a difference.
JPG is about as good as it gets. if they are tiff's then convert to jpg but
you will loose the color information.
It would be interesting though i don't think it would make a diffirence.
convert to image or iso? ummmmm......naa .... try it an see.