It's definitely between the latter two. Raubahn's washed up. Not entirely sure what Aymeric is capable of(we know he can take some serious abuse from what we've seen in HW, although he's a Pally in cannon so maybe that's expected). Merlwyb also seems like she'd be quite determined, but I don't think it'd be enough. Don't think we've ever seen Kan-E-Senna go on the offensive but she could probably try to stall everyone out. Lyse Hext is going to be gone in an instant.

Hien is also somewhat sturdy though and maybe it's because we've spent some time fighting with him in the MSQ(and as him), but I just feel like he's super capable.
Also, Vrtra is a fucking dragon. Nothing needs to be explained here.