The way they've worked for me the last two years is we negotiate how the levels will be chosen ahead of time. The ones that are unrestricted "you pick, I pick, random" . . . the second pick tends to be about as mean as the first. Those can be pretty wild if you're up for that sort of thing, but I prefer to at least talk about it a bit before hand. "Ok, you technically can pick anything, but keep in mind that I can always pick FRP if I want to.
"
The saner ones have been you pick, I pick off of the core list. And then what I like to do is if the dice give you something you've already played for the third level, whoever picked it can pick something else off the core list.
But I mean, I wouldn't write this things as hard and fast rules. I've played x4 vendettas, I've done "tour of skills" vendettas were we do blubird and then something really ratty and then power weapons only or something like that. I could imagine a fusion vendetta where you play Ugh and Purple and Ono or something.
Makes sense to be able to write your own terms. Just know what they are before agreeing. But "You pick, I pick, random off the core list" seems like pretty reasonable default terms.