Of course is used say that something is obvious. Is Bill Gates rich? Of course he is. Does a bear shit in the woods? Of course.
If it's going to be a great party and/or you've been looking forward to it for a long time, you might say "Of course, I wouldn't miss it for anything".
For sure means definitely, or without any doubt (undoubtedly). You could certainly say "for sure" as a response to that question too. "Are you going to the party?" For sure. Without any doubt.
If something is obvious, then there probably isn't any doubt about it. So they usually convey a very similar, almost identical meaning. I don't think that either is better than the other in this case.