Where to buy new 2016/2017/2018 macbook pro? Site or store?

Call the stores and ask them what they have in stock. We are users like you. We have no idea what store inventory may be.

If I was looking for an older Mac I would check out what is available refurbished from Apple. Refurbished Macs from Apple come with a warranty.

Refurbished Mac - Apple

I would not be buying it from eBay, Graigslist, etc.

Apple Retail Stores do not carry or stock refurbished Macs. The only way to obtain them is from the link BobTheFisherman provided. It is by far the best way to purchase a Mac at a substantial discount.

Avoid all other sources, with the possible exception of a face-to-face transaction with a private seller, and only if you are a very experienced Mac user who can thoroughly evaluate that Mac in person with the seller present, and only if the price compares very favorably to Apple's Refurbished price. And (goes without saying) full knowledge of the fact that if it breaks five minutes later, you're on your own.

There are reputable sellers of used equipment. They are very rare. I estimate less than five percent of eBay sellers properly prepare used Macs for sale, and it's been my experience their prices often exceed Apple's anyway. So why do people buy from them? Good question.

Do not ever set foot within a Best Buy. If for some reason you should ever inexplicably find yourself within one (in conjunction with a particularly evil and legally dubious fraternity hazing ritual for example) then proceed directly to the nearest exit.

There are plenty MBPs on Apple's Refurbished and Clearance page at the moment, even 2017 models.