Which site structure is better for SEO?

Hello,

I work at an e-commerce company which sells replacement parts, we carry thousands of products which fall into several categories & subcategories and at the same time, fit different brand, model and version items.

Given that scenario, which of the following site structures would work best to achive a high page rank:

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Structure 1
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- Use a set of select boxes to allow users to specify the brand, model and version of their item, then show them the list of categories that match, and finally (after the user clicks a category) show them the products related to that brand, model, version + category

- There is no category or subcategory pages

- There is no individual product pages (to avoid pagerank dilution)


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Structure 2
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- Allow the users to navigate the site by drilling down into category pages (Category > Subcategory > Products)

- Allow the users to navigate the site by drilling down using item features (Brand > Model > Version > Category > Products )

- Have category and subcategory pages.

- Link to category pages from the home page.



The first structure aims to increase pagerank by reducing the number of pages visible on the site, the second one aims to enhance user experience and give the sime some hierarchy, which one could work better for SEO?


I will really apprecite your ideas,
thanks