I think it is Fonseca, think he'll be interviewed tomorrow with expectation that he'll be offered the job. O'Neill and Allardyce have been getting the coverage due to being interviewed, but if either was going to get the job, why don't they have it now? Allardyce turned us down publicly, because we only wanted him short term. I'm not sure why you'd ask him back, as one of several interviews, unless you're rejecting him again. You don't really need to interview 2nd best candidate again, just give them job if you've changed your mind and they were someone you want.
You would interview the candidates from least to most likely, and 8/1 on Fonseca in betting market seems very generous to me. Tomorrow and Jim White telling us about an exciting new development. O'Neill and Allardyce are less popular choices, Fonseca fits more of the long term profile of Silva, who was obviously first long term pick of those available last time round.
We've seemed to chase public opinion around, but O'Neil is a non starter with fans, Allardyce also has a strong negative association with fans. Fonseca will likely be obscure enough to gain time to and hope from fanbase, other potential options look like favourable backlighting to me. Wouldn't be that suprised if Allardyce got it, but Fonseca is less likely to get despair and tears of the other candidates, more hope and intrigue and I think he's the more 'marquee signing'.