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The best place for them could be either, depending on a few factors. If you have little text on product pages, and their performance is poor as a result, then it may well be a good idea to use this text there. There's an argument that this would also be best for potential buyers of the product, who don't have to leave the page for further information. In the short term, this would likely get the most benefit from the content.
Longer term, your goal might be for product pages to perform well without the need for review content, in which case placing them elsewhere could be a good way of attracting a new audience for the products, in addition to visitors who find the product pages first.
There's no point SEOing if you don't do the best job once visitors arrive.
SEO isn't done for its own sake; it's part of the business plan, and the business target is not 'bums on seats' - it's making a profit.
Don't lose sight of the big picture.
I'm not a big one for "formulas" karim0028, but generally having seen quite a few implementations, I personally favor using one or more snippets on the product page (plus if possible, indicators of overall satisfaction/opinion). This helps the person who is considering buying the product, and also provides page text that can make the difference between a product page ranking well, or not.
Then those snippets can then link off to a complete page of reviews, which serves its own purpose.
FWIW, if there is always one or zero reviews (never two or more), I'd put them on the product page. Having an extra 500-1000 words doesn't really slow pageload times much and the benefits can be quite compelling.