There are people who try to answer this question as their postgrad topic of study, and still don't have a definite answer.
I prefer a combined approach of all possible joining types given their advantages in specific situations. This being said, one of the most useful fasteners in FRC is the rivet, as it can do just about everything (but isn't necessarily the best at everything). Bolting and welding are just as valuable, if you are equipped properly though.