Silva suffers from a degree of familiarity whereas Fonseca still retains the mystery of a 'foreign' manager and has that allure.
If Silva was still in work and potentially joining from a club abroad, then I think people would be more inclined generally to look on him in a more positive light.
They both share a lot in common. In reality there doesn't appear to be a lot between them although Fonseca showed he can set up a team to compete at UCL level and doesn't appear to have the defensive question marks that Silva does. Silva, on the other hand, has at least some experience of what it's like to manage here.
I have seen a lot of positive articles and praise floating about for Silva in the last week or so, which is encouraging to read. Whoever we might get in will be a gamble but even though we might be in for a rough teething period under either man, I am confident that either of them would prove to be an upgrade on Allardyce in the medium term.