I vote #2. #3 gives them too much credit, and #1 not enough.

Although it may not be so much that real monsters catch more eyeballs as that messing with the formula (in a reboot) catches more eyeballs. By now, I've seen enough direct-to-video modern Scoobies that I expect them to be supernatural (as well as inferior in other ways), so maybe next time they'll go back to fake monsters?

Scooby-Doo and the Witch's Ghost is probably the worst. It's not just that the witch is real, which as I said I expect now, but its (positive!) references to Wicca are so uninformed and trashy that it's actually an insult to Wiccans too.

Edit: Possibly Scooby-Doo! Mystery Incorporated is exactly this return to fake monsters. I don't know, I haven't seen it. Since it has an ongoing story arc, they may decide to make a monster real in the end.