If Josie keeps good on her word, she will be the next to leave because she refuses to pee in the closet. I imagine her bladder has to be about ready to burst by now. Besides, Josie is the only one that's safe from elimination, so she has less incentive to stay.
Letty has shown she's in it to win it and crazy so I'm leaning towards her winning. She also doesn't mind starving so hunger won't be that big of a deal. That being said, she's already rail thin so she would start feeling like complete trash after a couple of days.
Sylvia has experience living in rough environments and I think she recently realized she's the least popular fish and really needs a win. She also isn't safe from elimination and Jon shook her baby (plus it seems she has stopped caring for it lately), so she probably won't win the baby challenge either. She doesn't seem as crazy as Letty, but if she can get past the initial hunger pangs, she could actually sail through this easier than Letty or Vance since she has extra fat for her body to use. For those who don't know, once you get over the initial hunger pangs and start fasting for a couple of days, you don't feel hungry anymore and you actually get a boost of feel good energy.
Vance is the least likely to win. Despite his big cringy speeches, he hasn't shown much motivation and appears to want to leave. That speech he gave to his gf ("If anything bothers you just call and I'll leave!") felt like an excuse for him to leave without looking like a pussy. "Oh, I wanted to stay, but my girlfriend asked me to come home, and I love her so much, so I had to do it." I haven't seen him do anything that shows he really wants to win.