Oh wow, what a thread. I pesonally don't like sidekicks generally, because in ma opinio sidekicks always have a comic side: the hero does something and the sidekick comments on it. That's not my cup of tea, sorry, that's not my glass of whisky.
A classical sidekick is someone like Barrica or Whisky. I don't like characters like this in my SWs.
Sidekicks that are tolerable, are characters, who don't play such a big role, or don't occupy a big space in the movie, like the old man in Arriva Sartana. That's OK for me. Like the No1 on your list - Silvanito.
Maybe this would be my No1 siedekick as well, since he's not funny.
So, to make a list of my own, I have ti look for those un-funny sidekicks...