If the ad is about the product, then link to the product page.
I click because of the product ad and my interest in the product, so I expect to see it after the page finishes loading. Don't expect people to look for it, or scroll down the page, or make an extra click. You don't want to risk your visitors clicking away.
Always heard to make it the fewest clicks possible for people to give you money.
Product page, people are lazy, everything should be little distraction and straight to what you’ve advertised
Product
If the ad is about the product, then link to the product page. I click because of the product ad and my interest in the product, so I expect to see it after the page finishes loading. Don't expect people to look for it, or scroll down the page, or make an extra click. You don't want to risk your visitors clicking away.