Allardyce would bring stability and after the start we had this season, that would be reassuring. However, stability doesn't necessarily mean progress and at what point would we let go? We could keep him for the next 5 years, finishing mid-table, but we'd be stagnating.
We do need to have a replacement lined up before we get rid of Sam, though. The 'get rid of him right now' mentality is stupid because we'd then be rudderless, again.
As for Silva or Fonseca, who knows? It feels a bit like Porto guy all over again. I don't know a huge amount about Fonseca, except that he wore a Zorro mask and they beat City in the CL this season. Otherwise, he's achieving about what is expected with a good team in a poor league (and I've just learned that Metalist Kharkiv ceased to exist in 2016 and Dnipro were relegated last season).
Silva doesn't really inspire much confidence either tbh. It does amuse me that people talk about ambition and then laud the ex-Hull and Watford manager as the saviour! No, he didn't take Hull down, but it's still a blot on his copybook. And Watford may have looked decent for 10 matches, but we fluttered our eyelashes and it all went to pot - is that really all it takes?
If I had to pick, I'd go with Fonseca over Silva, based on him managing at a higher level. Either would be a risk, but it's one we need to take sooner or later and it'd hopefully breath life into a failing squad and weary fans.