The only justification I consider reasonable for Machete (or Rister) order is when you’re with someone who hasn’t seen them before and insists on including the prequels in their first viewing (which is what the situation was with a couple of the people in the group I did my pre-TFA marathon with). I would never, ever want to start a new viewer on any of the prequels, and doing them all at the end after we’ve already seen all of the movies I actually like is such a demoralizing prospect. If the other party can be persuaded not to do it all in one go, I recommend marathoning the OT (and now I guess TFA) and then coming back to the PT at a later date just to get an idea of what I now think of as the bad old days.

For my own viewings, if I’m expanding things beyond the OT (which I sometimes do, since I find watching the PT with like-minded friends and creating our own commentary once in a long while to be an enjoyable experience in its own right) and I don’t need to take newbies into consideration, I tend to prefer to spread it out over a couple days: be baffled by the PT on day one, be delighted by the OT on day two, and for now, either tack TFA onto the end of the second day or watch it on its own soon after. If I’m in charge of programming on whatever my gang’s pre-VIII marathon ends up being, I’m thinking PT two weekends before VIII, OT the following weekend, and then TFA earlier in the day before we head to the theater.