The Divimax, 2-Disc Edition of
Halloween is the best, featuring a commentary track and several documentaries.
A Divimax version of Halloween 4 was recently released, featuring a beautiful transfer. The same has been done with
Halloween 5.
Besides those three releases, you'll have to go with the only option for the rest of the series: bare-bones, average transfer releases.
**Note: Universal is releasing a double feature DVD containing
Halloween II and
Halloween III: Season of the Witch. You might save some money there if you don't mind the double bill.