In mountainbiking, tire traction is a key element of a good riding. Traction is about putting resistant to free spinning wheel (imagine slick tire on muddy trail). The amount of traction that you really need is just merely by being able to put on resistant to the ground, thus enable you to move forward. While having more traction may seem better, it also comes with more resistant to trail thus increase load to your pedaling effort (imagine 2.5" for cross country ride or any knobbie tire on tarmac ride up to Genting Sempah).
I can't give recommendation on "best" tire simply I not a person to refer to on this matter. I believe that there is no single tire thread and pressure will suit best through out a course of MTB outing. It's a matter of striking the balance of pros and cons to cater most situation.
p.s: An element of correct tire mounting is also important.