From a purely organic perspective, the best way to assess a site's performance and compare it to its main competitors is through Visibility Indexes.

Here the site's visibility is trended over time, as well as its competitors and determine whether its organic performance is going up or down by analysing specific categories. Click 'Site' above the index chart and select your own site:

Now the site's performance for each of the categories is included in the visibility index:

After resetting the index, click the filter button and select the subcategory or subcategories to explore further:

Now, the index compares your site with your competitors for a specific category or categories:

Share of Voice is used to look at the rankings from a commercial point of view. This means the rankings for each search term will weigh differently depending on each search term's search volume, CPC, and competition.

Using the Share of Voice Timeline tool to analyse a Market Intelligence of choice will reveal how well your site performs for a category over time and how it compares to its competitors.

Here you can see how your site's share of voice or share of the market has trended over time, as well as the top performers in that category:

Drill down to analyse subcategories by clicking on them: