also comes down to feel. I will always have a screen protector on any phone I own. I happen to like the ZAGG Invisoshield protectors. They work well, do not change color with age, and they have a lifetime warranty. if they get scratched, ZAGG will send you a new one.

Also, I do not notice a loss of responsiveness when compared to others' iPhones who have different protectors or none at all. However, without lab experiments, this is mostly subjective anyway.

You will always be better off with a screen protector than without - if your goal is to keep the screen pristine.