AppleCare+ is the extended warranty coverage provided by & through Apple. Here is a link to information about AppleCare+:
AppleCare Products - Mac - Apple
I have no idea what Protect Plus is, but I suspect it is the store's own warranty plan. You have to be very careful with store warranty coverage because they will likely dictate who will repair the device (perhaps even will require mailing it somewhere for repair). It will most likely be an unauthorized repair which these days is extremely risky because Apple pairs most parts to the Logic Board which makes it nearly impossible for any unauthorized independent repair shops to repair a Mac these days. I would avoid such independent warranty/insurance plans because there are usually some "gotchas" in them with loopholes in the fine print.
I'm not even sure if AC+ is even worthwhile since you must pay for the extended coverage, but to take advantage of the accidental damage portion, you still must pay out money for a flat rate (although discounted) for repairing accidental damage. If you look at the AC+ accidental damage repair rates you will see the following which will need to be paid each time you repair the laptop for accidental damage:
- $99 US For any issue with the laptop's built-in Display Assembly (aka the "lid")
- $299 US For any other issue with the laptop...includes any parts located in the base of the laptop including the Top Case/Palmrest Assembly and everything beneath it such as Logic Board, I/O Boards, etc.
- $398 US For repairs where both the Display Assembly is damaged and any item in the base is damaged (this is not really clear in Apple's documentation, but if you read it carefully it is kind of implied)
AC+ coverage provides you with free repairs for normal failures while AC+ is active, but you must still pay a discounted fee for any accidental damage repairs. Keep in mind that Apple determines whether a fault is caused by "natural" causes or from accidental damage...different techs can interpret things a bit differently. Do the math for the costs involved with AC+ and the cost to replace the laptop with a new one. Out of warranty repairs are expensive as well.
I almost always avoid extended warranty plans, but that is just me. Others do feel that AC+ coverage is a good deal.....I know several respected forum contributors who highly recommend AC+ for users. At least you know AC+ coverage is provided by Apple.....it is Apple or an Apple Authorized Service Provider who will be performing official authorized repairs on AC+ covered devices.