You can make a case for all of them but I want to hear your opinions while I eat my Frankenberry cereal and watch the original series.
Remember! Slasher flicks have Tropes: the jock, the wh*re, the nerd, the stoner, and the Virgin (who is the Final Girl.)
(Sometimes the nerd and the stoner are combined.)
The wh*re is presented as a cheerleader but tbh I don’t like saying cheerleaders are that stereotype

let’s call her the Worldly and Sexually Educated Character.
The rules of horror flicks from the 80s being, of course, that sex = sin, and you will be murdered
There’s also the Token Minority, but that’s not always present.
About to derail into a criticism of Hollywood for leaning hard into the notion that a woman (actresses specifically) can only be virgins, mothers, or wh*res. They did it well up into the 2000s and some directors even openly admitted to playing it up.
But it’s becoming a little less pervasive
Also this episode of Scooby Doo, they come face to face with two dudes in masks and their collective first response is “GHoSTS!!!”
Y’all it’s episode 2, season 1
They are working through serious traumas not shown in the series.
Thats tough, see I wanna say Velma or Scooby himself, but dogs usually survive horror/slasher movies. So, that would drop it down to Velma, who is also the nerd type but usually the most savvy with figuring things out. My counter argument is she would likely get killed trying to prove something. This is a lot harder than it should have been.
Ooooof good point about the dog
In my scooby doo slasher, let’s say the dog DOESN’T die. (But isn’t necessarily the final girl.)
Another pervasive problem with cinema! Killing the dog for a cheap visceral reaction in the audience!
THIS I hate when that happens in movies for a reaction. The first time I saw that in some movie Marky Mark was in in the 90s it felt physically ill. I cant stomach animals being harmed. People sure, animals no. Thats a cheap shot.
The other argument I could see for the Scooby gang would be Daphne, and I mostly say this from the recent Happy Halloween Scooby Doo, she's smart as hell even if she acts bubbly. She can find ways to get what she wants and notices details others don't, she would be my second choice.