I don't know what is the best, but usually for data I use ISO format.
To burn a DVD with a ROM booktype first of all you need a burner able to change booktype (liteon, benq, plextor are some examples), and must use a +R (plus) disc, because bitsetting is not possible with -R (dash) media.
Burning a disc with ROM booktype is useful only to increase the compatibility of a DVD (usually video) with older standalone DVD players, not to increase quality.
Quality of a burn depends largely on the combination burner/firmware/media used. To know what is the best for your burner the only way is experimenting with the media available in your country (for example I've never found a pastel verbatim DVD in my area). The ROM booktype don't influence the quality of a burn.
Hope this can help