Depends on the model, and depends on how much you value hassle free repairs. Depends on how willing you are to carry around a busted phone to save a few bucks. Also depend on how much you trust your case.

If you break the back glass of your iPhone 14 Pro you are absolutely fucked and cannot get it fixed for less than $500.....but replacing the back glass on an iPhone 14 is only $169. Replacing the front glass on the basic iPhone 14 is $279, but on the 14 Pro Max it is $379. If you go with the case, you had better damn well trust that it will protect both the front and back without fail.

If you have AppleCare+, repairing the front or back glass on any model is only $29 per incident.

I asbsolutely love going without a case, so I just pay the $100-120/year and call it a day. When you get the back glass replaced they pretty much give you an entirely new phone, so I've gotten two replacements for a relatively small deductible. I never have to worry about dropping or mishandling the phone.

The only thing I can say for certain is not to pay for carrier-provided insurance (unless it includes AppleCare+). Deductibles are expensive, and they will not repair or replace with the same speed as an Apple Store.

I guess you also ought to consider how close you are to an Apple Store (or Apple-approved repair centers like Best Buy). You will have to take your phone to these locations for repairs (or mail it off if there aren't any near year).