Observer pattern in C#, which is the most responsive? Handler VS thread

I have read all the posts about the implementation of Observer Pattern by Event about .NET and C#

I'm wondering in a real scenario which of these things are more responsive.

In .NET and C# I can avoid Observer Pattern using Events. Or I can implement a Observer Pattern by Event.

In addition I can build a Observer Pattern using threads, actually I have already implemented this.

I have a remote service who can send tons of information and Observer/Events would be under stress. I mean the message from the remote service have to publish as soon as is possible to UI

Which is the most responsive around the whole application?