It depends on many things: (1) case facts; (2) insurance coverage issues; (3) the attitude of the plaintiff, their expectations, and reasonableness; (4) the attitude of the defendant and their reasonableness; (5) the skill of the lawyers for both sides; (6) the reasonableness of the insurance adjuster for the defendant; and (7) in cases of a mediator, whether the mediator or arbitrator is skillful.
Mediation is usually non-binding. Sometimes arbitration is binding (you can't just walk away if your expectations are not met). I'm not sure what "neutral evaluation" is. Usually, good attorneys on both sides can work these things if the insurance company and the parties are reasonable. Sometimes the lawyers aren't mature enough for this, though.
You've asked a very broad question. I'm sure other attorneys on avvo will have a robust response and will come at this from various interesting angles.